Our bodies can obtain vitamin D from diet and make it from sun exposure. Even with these two routes for obtaining vitamin D, however, inadequate vitamin D is common, and deficiencies can be found on all continents, in all ethnic groups, and across all ages—a major concern, given the many ways that vitamin D helps protect our health. (1) There are a number of factors that increase the risk of having inadequate vitamin D, among them, lifestyle, sunscreen use, geographic location, skin tone, age, and body weight.

• Lifestyle: People who spend less time outdoors, or who cover up with clothing when they are outdoors, get less exposure to the sun, so they make less vitamin D. (1)
• Sunscreen Use: Correctly-applied sunscreen blocks the harmful ultraviolet B rays that cause skin cancer, but it also blocks most of the skin’s production of vitamin D. So people who use sunscreen daily are more likely to be low in vitamin D. (1) But don’t ditch the sunscreen: The American Academy of Dermatologists says that sunlight exposure to unprotected skin increases the risk of skin cancer, and that there’s no safe level of sunlight exposure that allows you to make vitamin D without increasing skin cancer risk. Their advice? Use sunscreen or other sun protection daily, skip the tanning booths, and get your vitamin D from diet or supplements. (2) Some Vitamin D experts take issue with the American Academy of Dermatologists’ hard line on sun exposure, and they recommend a more moderate option: Put sunscreen on your face, and allow your arms and legs to get a small amount of unprotected sun exposure—say, 15 minutes max—before applying sunscreen or covering up. It’s still a matter of scientific debate.
• Geographic Location and Season: In the summer, if you sat out in a bathing suit on a sunny afternoon for long enough to turn your skin slightly pink, you could make plenty of vitamin D. Yet during the late autumn and winter, people who live at higher latitudes produce little or no vitamin D from the sun, because the sun is at too low an angle in the sky. In the northern hemisphere, people who live in Boston (U.S.), Edmonton (Canada), and Bergen (Norway) can’t make enough vitamin D from the sun for 4, 5, and 6 months out of the year. (3) In the southern hemisphere, residents of Buenos Aires (Argentina) and Cape Town (South Africa) can make far less vitamin D from the sun during their winter months (June through August) than they can during their spring and summer. (3) The body stores vitamin D from summer sun exposure, but it must last for many months. By late winter, many people in these higher-latitude locales are deficient. (1)
• Skin Tone: People who have a darker skin tone have more melanin in their skin, and this pigment is a “natural sunscreen” that slows down skin production of vitamin D. (3)  This the main reason why African Americans are more likely to be low in vitamin D. (4)
• Age: The ability to make vitamin D in the skin drops as we age, and is one of the reasons why older individuals are more likely to have low vitamin D levels. (1)
• Body Weight: People with excess body fat have lower vitamin D levels, so those who are overweight or obese have a higher risk of having inadequate vitamin D.  (1, 5, 6)

The bottom line: Low vitamin D can be found in all ethnic and age groups, around the world, for a host of reasons. Even if you are taking a standard multiple vitamin, the amount of vitamin D in most vitamins (400 IU) is not enough to prevent low blood levels. If you suspect that you are at risk of vitamin D deficiency, you can ask your physician to order a blood test for vitamin D.

Vitamin D Deficiency: A Global Concern

If you live north of the line connecting San Francisco to Philadelphia and Athens to Beijing, odds are that you don’t get enough vitamin D. The same holds true if you don’t get outside for at least a 15-minute daily walk in the sun. African-Americans and others with dark skin, as well as older individuals, tend to have much lower levels of vitamin D, as do people who are overweight or obese.

Worldwide, an estimated 1 billion people have inadequate levels of vitamin D in their blood, and deficiencies can be found in all ethnicities and age groups. (1-3)  Indeed, in industrialized countries, doctors are even seeing the resurgence of rickets, the bone-weakening disease that had been largely eradicated through vitamin D fortification. (4-6)

Why are these widespread vitamin D deficiencies of such great concern? Because research conducted over the past decade suggests that vitamin D plays a much broader disease-fighting role than once thought.

Being “D-ficient” may increase the risk of a host of chronic diseases, such as osteoporosis, heart disease, some cancers, and multiple sclerosis, as well as infectious diseases, such as tuberculosis and even the seasonal flu.

Currently, there’s scientific debate about how much vitamin D people need each day. The Institute of Medicine, in a long-awaited report released on November 30, 2010 recommends tripling the daily vitamin D intake for children and adults in the U.S. and Canada, to 600 IU per day. (7) The report also recognized the safety of vitamin D by increasing the upper limit from 2,000 to 4,000 IU per day, and acknowledged that even at 4,000 IU per day, there was no good evidence of harm. The new guidelines, however, are overly conservative about the recommended intake, and they do not give enough weight to some of the latest science on vitamin D and health. For bone health and chronic disease prevention, many people are likely to need more vitamin D than even these new government guidelines recommend.

Vitamin D Sources and Function

Vitamin D is both a nutrient we eat and a hormone our bodies make. Few foods are naturally rich in vitamin D, so the biggest dietary sources of vitamin D are fortified foods and vitamin supplements. Good sources include dairy products and breakfast cereals (both of which are fortified with vitamin D), and fatty fish such as salmon and tuna.

The body also manufactures vitamin D from cholesterol, through a process triggered by the action of sunlight on skin, hence its nickname, “the sunshine vitamin.”  Yet some people do not make enough vitamin D from the sun, among them, people who have a darker skin tone, who are overweight, who are older, and who cover up when they are in the sun. (1)

Correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent. (8) And not all sunlight is created equal: The sun’s ultraviolet B (UVB) rays—the so-called “tanning” rays, and the rays that trigger the skin to produce vitamin D—are stronger near the equator and weaker at higher latitudes. So in the fall and winter, people who live at higher latitudes (in the northern U.S. and Europe, for example) can’t make much if any vitamin D from the sun. (8)

Vitamin D helps ensure that the body absorbs and retains calcium and phosphorus, both critical for building bone. Laboratory studies show that vitamin D can reduce cancer cell growth and plays a critical role in controlling infections. Many of the body’s organs and tissues have receptors for vitamin D, and scientists are still teasing out its other possible functions.

New Vitamin D Research: Beyond Building Bones

Several promising areas of vitamin D research look far beyond vitamin D’s role in building bones. And, as you might expect, the news media release a flurry of reports every time another study links vitamin D to some new ailment. These reports can be confusing, however, because some studies are stronger than others, and any report needs to be interpreted in the light of all other evidence. More answers may come from randomized trials, such as the VITamin D and OmegA-3 TriaL (VITAL), which will enroll 20,000 healthy men and women to see if taking 2,000 IU of vitamin D or 1,000 mg of fish oil daily lowers the risk of cancer, heart disease, and stroke.

Here, we provide an overview of some of the more promising areas of vitamin D research, highlighting the complex role of vitamin D in disease prevention—and the many unanswered questions that remain.

Vitamin D and Bone and Muscle Strength

Several studies link low vitamin D levels with an increased risk of fractures in older adults, and they suggest that vitamin D supplementation may prevent such fractures—as long as it is taken in a high enough dose. (9-13)

A summary of the evidence comes from a combined analysis of 12 fracture prevention trials that included more than 40,000 elderly people, most of them women. Researchers found that high intakes of vitamin D supplements—of about 800 IU per day—reduced hip and non-spine fractures by 20 percent, while lower intakes (400 IU or less) failed to offer any fracture prevention benefit. (13)

Vitamin D may also help increase muscle strength, which in turn helps to prevent falls, a common problem that leads to substantial disability and death in older people. (14-16)  Once again, vitamin D dose matters: A combined analysis of multiple studies found that taking 700 to 1,000 IU of vitamin D per day lowered the risk of falls by 19 percent, but taking 200 to 600 IU per day did not offer any such protection. (17)

A recent vitamin D trial drew headlines for its unexpected finding that a very high dose of vitamin D increased fracture and fall risk in older women. (18) The trial’s vitamin D dose—500,000 IU taken in a once-a-year pill—was much higher than previously tested in an annual regimen. After up to 5 years of treatment, women in the vitamin D group had a 15 percent higher fall risk and a 26 percent higher fracture risk than women who received the placebo.

It’s possible that giving the vitamin D in one large dose, rather than in several doses spread throughout the year, led to the increased risk. (18) The study authors note that only one other study—also a high-dose, once-a-year regimen—found vitamin D to increase fracture risk; no other studies have found vitamin D to increase the risk of falls. Furthermore, there’s strong evidence that more moderate doses of vitamin D taken daily or weekly protect against fractures and falls—and are safe.

So what is the significance of this study for people who want to take vitamin D supplements? A reasonable conclusion would be to continue taking moderate doses of vitamin D regularly, since these have a strong safety record, but to avoid extremely high single doses. This recent finding does present a challenge to scientists who will work to understand why the extreme single dose appears to have adverse effects.

Vitamin D and Heart Disease

The heart is basically a large muscle, and like skeletal muscle, it has receptors for vitamin D. (19) So perhaps it’s no surprise that studies are finding vitamin D deficiency may be linked to heart disease. The Health Professional Follow-Up Study checked the vitamin D blood levels in nearly 50,000 men who were healthy, and then followed them for 10 years. (20) They found that men who were deficient in vitamin D were twice as likely to have a heart attack as men who had adequate levels of vitamin D. Other studies have found that low vitamin D levels were associated with higher risk of heart failure, sudden cardiac death, stroke, overall cardiovascular disease, and cardiovascular death. (21-24) How exactly might vitamin D help prevent heart disease? There’s evidence that vitamin D plays a role in controlling blood pressure and preventing artery damage, and this may explain these findings. (25) Still, more research is needed before we can be confident of these benefits.

Vitamin D and Cancer

Nearly 30 years ago, researchers noticed an intriguing relationship between colon cancer deaths and geographic location: People who lived at higher latitudes, such as in the northern U.S., had higher rates of death from colon cancer than people who live closer to the equator. (26) Many scientific hypotheses about vitamin D and disease stem from studies that have compared solar radiation and disease rates in different countries. These can be a good starting point for other research but don’t provide the most definitive information. The sun’s UVB rays are weaker at higher latitudes, and in turn, people’s vitamin D levels in these high latitude locales tend to be lower. This led to the hypothesis that low vitamin D levels might somehow increase colon cancer risk. (2)

Since then, dozens of studies suggest an association between low vitamin D levels and increased risks of colon and other cancers. (1,27)  The evidence is strongest for colorectal cancer, with most (but not all) observational studies finding that the lower the vitamin D levels, the higher the risk of these diseases. (28-38) Vitamin D levels may also predict cancer survival, but evidence for this is still limited. (27) Yet finding such associations does not necessarily mean that taking vitamin D supplements will lower cancer risk.

The VITAL trial will look specifically at whether vitamin D supplements lower cancer risk. It will be years, though, before it releases any results. It could also fail to detect a real benefit of vitamin D, for several reasons: If people in the placebo group decide on their own to take vitamin D supplements, that could minimize any differences between the placebo group and the supplement group; the study may not follow participants for a long enough time to show a cancer prevention benefit; or study participants may be starting supplements too late in life to lower their cancer risk. In the meantime, based on the evidence to date, 16 scientists have circulated a “call for action” on vitamin D and cancer prevention: (27) Given the high rates of vitamin D deficiency in North America, the strong evidence for reduction of osteoporosis and fractures, the potential cancer-fighting benefits of vitamin D, and the low risk of vitamin D supplementation, they recommend widespread vitamin D supplementation of 2000 IU per day. (27)

Vitamin D and Immune Function

Vitamin D’s role in regulating the immune system has led scientists to explore two parallel research paths: Does vitamin D deficiency contribute to the development of multiple sclerosis, type 1 diabetes, and other so-called “autoimmune” diseases, where the body’s immune system attacks its own organs and tissues? And could vitamin D supplements help boost our body’s defenses to fight infectious disease, such as tuberculosis and seasonal flu? This is a hot research area and more findings will be emerging.

Vitamin D and Multiple Sclerosis: Multiple sclerosis (MS) rates are much higher far north (or far south) of the equator than in sunnier climes, and researchers suspect that chronic vitamin D deficiencies may be one reason why. One prospective study to look at this question found that among white men and women, those with the highest vitamin D blood levels had a 62 percent lower risk of developing MS than those with the lowest vitamin D levels. (39) The study didn’t find this effect among black men and women, most likely because there were fewer black study participants and most of them had low vitamin D levels, making it harder to find any link between vitamin D and MS if one exists.

Vitamin D and Type 1 Diabetes: Type 1 diabetes is another disease that varies with geography—a child in Finland is about 400 times more likely to develop it than a child in Venezuela. (40) Evidence that vitamin D may play a role in preventing type 1 diabetes comes from a 30-year study that followed more than 10,000 Finnish children from birth: Children who regularly received vitamin D supplements during infancy had a nearly 90 percent lower risk of developing type 1 diabetes than those who did not receive supplements. (41)  Other European case-control studies, when analyzed together, also suggest that vitamin D may help protect against type 1 diabetes. (42) No randomized controlled trials have tested this notion, and it is not clear that they would be possible to conduct.

Vitamin D, the Flu, and the Common Cold: The flu virus wreaks the most havoc in the winter, abating in the summer months. This seasonality led a British doctor to hypothesize that a sunlight-related “seasonal stimulus” triggered influenza outbreaks. (43) More than 20 years after this initial hypothesis, several scientists published a paper suggesting that vitamin D may be the seasonal stimulus. (44) Among the evidence they cite:

• Vitamin D levels are lowest in the winter months. (44) 
• The active form of vitamin D tempers the damaging inflammatory response of some white blood cells, while it also boosts immune cells’ production of microbe-fighting proteins. (44) 
• Children who have vitamin D-deficiency rickets are more likely to get respiratory infections, while children exposed to sunlight seem to have fewer respiratory infections. (44) 
• Adults who have low vitamin D levels are more likely to report having had a recent cough, cold, or upper respiratory tract infection. (45)

A recent randomized controlled trial in Japanese school children tested whether taking daily vitamin D supplements would prevent seasonal flu. (46) The trial followed nearly 340 children for four months during the height of the winter flu season. Half of the study participants received pills that contained 1,200 IU of vitamin D; the other half received placebo pills. Researchers found that type A influenza rates in the vitamin D group were about 40 percent lower than in the placebo group; there was no significant difference in type B influenza rates. This was a small but promising study, and more research is needed before we can definitively say that vitamin D protects against the flu. But don’t skip your flu shot, even if vitamin D has some benefit.

Vitamin D and Tuberculosis: Before the advent of antibiotics, sunlight and sun lamps were part of the standard treatment for tuberculosis (TB). (47) More recent research suggests that the “sunshine vitamin” may be linked to TB risk. Several case-control studies, when analyzed together, suggest that people diagnosed with tuberculosis have lower vitamin D levels than healthy people of similar age and other characteristics. (48)   Such studies do not follow individuals over time, so they cannot tell us whether vitamin D deficiency led to the increased TB risk or whether taking vitamin D supplements would prevent TB. There are also genetic differences in the receptor that binds vitamin D, and these differences may influence TB risk. (49) Again, more research is needed. (49)

Vitamin D and Risk of Premature Death

A promising report in the Archives of Internal Medicine suggests that taking vitamin D supplements may even reduce overall mortality rates: A combined analysis of multiple studies found that taking modest levels of vitamin D supplements was associated with a statistically significant 7 percent reduction in mortality from any cause. (50) The analysis looked at the findings from 18 randomized controlled trials that enrolled a total of nearly 60,000 study participants; most of the study participants took between 400 and 800 IU of vitamin D per day for an average of five years. Keep in mind that this analysis has several limitations, chief among them the fact that the studies it included were not designed to explore mortality in general, or explore specific causes of death. More research is needed before any broad claims can be made about vitamin D and mortality. (51)

Remember when a total cholesterol reading of under 200 was the standard for judging cardiovascular health? Today, of course, we know that it's the components of cholesterol (LDL, HDL, the size of those cholesterol particles, and triglycerides) that are much more predictive of heart health. Well, our understanding of total weight and its effects upon your heart has evolved in similar fashion. It's not your total weight but the characteristics of that weight—how much is fat and where it's deposited—that matter most.

Surprised? Thank the scientists at the Mayo Clinic, who are behind this recent discovery. After comparing various health markers with the weights and body mass index numbers of thousands of adults, they found that more than half of those with normal weights and BMIs actually had "high body-fat percentages as well as heart and metabolic disturbances." In other words, they had the same risks of coronary disease, diabetes, and other chronic illness as people who weighed much more.

This research, and its sobering implications for millions of Americans, led to the establishment of a new condition called normal weight obesity (NWO). This is more than just the latest fat phobia. It's worth paying attention to because the accumulation of fat in the body, especially in the belly and around internal organs, causes low-level inflammation that gradually damages tissue and blood vessels. (Think of it as metabolic rust.) So even though your weight or BMI may be within acceptable limits for your height and age, don't be lulled into a false sense of security. Do your own analysis, starting with these steps:

1. Stop being preoccupied with pounds. As with total cholesterol, total weight is just one general assessment of your health. Yes, people who are trying to lose weight are more likely to succeed if they weigh themselves often. But seeing numbers that are within a healthy BMI range may actually disguise your heart disease risk. Keep them in perspective.

2. Measure your body fat. For a quick estimate of this key factor, wrap a cloth measuring tape around your naked waist just above your belly button. If your weight is fairly normal but the number you see above your navel is 35 inches or more (40+ inches for men), you may have NWO. For a more exact reading, ask your doctor (or health club) to measure your body fat. This can be done using a variety of noninvasive methods. If it's higher than 30 percent (20 percent for men), you likely have NWO.

3. Get a blood test. Ask your doctor to order a thorough blood analysis at your next physical. Warning signs of NWO include low HDL (total cholesterol and LDL may be normal), along with elevated triglycerides, blood sugar, and blood pressure.

4. Target belly fat. If you're diagnosed with NWO, take aim at visceral fat. Despite how entrenched it may seem, you can lose it. The keys are: Avoid the white stuff (white bread, rice, pasta, and other refined carbohydrates). Add monounsaturated fats, which target belly fat, to your diet. And do interval exercises to burn more fat and strength-training to build lean body mass.

5. Keep tracking fat. Just as you hop on the scale to keep tabs on your weight, do the same with your body fat. Have it measured periodically at your doctor's office or health club. Or just observe the notches where your belt buckles.

Conversely, if you're considered overweight by current standards, there may be some good news here. If your body-fat percentage is lower than 30 percent (20 percent for men) and your blood chemistry is normal, then you are among the "fat and fit." (Many athletes are in this category.) Continue to eat smart and exercise, but accept your body for what it is and know you're not unhealthy because of it. Feeling fat and feeling healthy are no longer mutually exclusive.

More Heart-Healthy Advice

Staying hydrated is one simple way to keep blood pressure in the safe zone.

The foods we eat can affect our risk of developing certain types of cancer. High energy and high fat diets can lead to obesity and are generally thought to increase the risk of some cancers. Plant-based diets high in fresh fruits, vegetables, legumes and wholegrain foods may help to prevent cancer.

Diet is just one of the lifestyle factors that influence the risk of developing cancer. Smoking, obesity, alcohol, sun exposure and physical activity levels are also important. Although some foods can affect cancer risk, there is no evidence that specific foods can cause or cure cancer.

Food and some common cancers
Some common cancers (and how they are affected by what we eat) include:

• Lung cancer – this is the leading cause of death from cancer in the world and smoking is mostly responsible. There is convincing evidence that diets high in vegetables and fruits are protective against lung cancer. It is thought that compounds called carotenoids (present in significant amounts in fruits and vegetables), as well as vitamin E, are probably responsible for some of this effect. However, the use of antioxidant supplements, such as beta-carotene and vitamin E, has not been proven to be effective in either prevention or treatment of lung cancer and may, in fact, increase the risk of developing cancer in those who smoke. While fruits and vegetables may offer some degree of protection, not smoking in the first place is by far the best prevention.

• Breast cancer – this is the most common type of cancer in women in the world. There is an increased risk of breast cancer with factors such as rapid early growth, greater adult height and weight gain in adulthood. Much of the risk of developing breast cancer involves factors that influence oestrogen levels during a woman’s reproductive life, such as age of menarche (first period), number of pregnancies and breastfeeding practices. Post menopausal women who are carrying too much weight, especially around their middle, have more than twice the average risk of breast cancer. Diets high in mono-unsaturated fat and high in vegetables and fruits may reduce the risk, while alcohol consumption increases the risk.

• Prostate cancer – a quarter of all new cancers diagnosed in men in UK is prostate cancer. Vegetables, soy in particular may decrease the risk, while a high fat diet that comprises mostly animal fat sources (such as dairy products, fatty meats and takeaway foods) may increase the risk. Lycopene is a potent antioxidant found in tomatoes, tomato-based products, watermelon and strawberries. It may also help lower the risk of prostate cancer.

• Bowel cancer – this is the fourth most common cancer in the world. Up to 70 per cent of cases can be prevented by following a healthy lifestyle. Keeping a healthy weight, being physically active and a diet high in vegetables and fibre are protective, while consuming a large amount of red meat (especially processed meat) and alcohol may increase the risk.

Foods to ‘eat less’
Foods to limit in your diet or eat less of include:

• Fatty processed red meats

• Highly processed foods that are low in fibre

• Heavily salted and pickled foods.

Foods to ‘eat more’
The strongest protective anti-cancer effect has been shown with:

• Vegetables, especially raw vegetables or salads

• Leafy green vegetables

• Carrots

• Tomatoes

• Citrus fruits

• Cruciferous vegetables like broccoli, cabbage, brussels sprouts, bok choy and other Asian greens.

Include more of these vegetables and fruits in your diet along with other varieties.

Seven a day
Eating seven or more serves daily of a variety of grains, grain products, legumes, roots and tubers will also provide protective benefits against cancer. The less processed the grains, the better. Diets high in refined starch and refined sugar may increase the risk of stomach cancer and bowel cancer.

Meat and bowel cancer
There is now convincing scientific evidence that eating processed meat increases bowel cancer risk. The World Cancer Research Fund (WCRF) has recently recommended that people avoid eating processed meat. Processed meats are any meat that has been preserved by curing, salting or smoking, or by adding chemical preservatives. These meats include hot dogs, ham, bacon and some sausages and burgers.

It is recommended that children are not given processed meats at all. This is because many of the habits we develop as children last into adulthood. Substitutes for processed meats that are recommended for children include poultry or fish, low fat cheese or small amounts of lean meat.

The WCRF also recommends limiting the amount of fresh red meat we eat to 500g (cooked weight) a week. This is because there is convincing evidence that red meat also increases a person’s risk of bowel cancer.

Some research suggests that eating burnt or charred meat may increase cancer risk, but the evidence is unclear.

Fats and cancer
There has been a great deal of interest in the possible association between fat and cancer. Current evidence does not indicate a direct link between fat intake and particular types of cancer (with the possible exception of prostate cancer). However, a high fat diet may lead to obesity, which is a risk factor for several cancers including cancer of the colon, breast, kidney, oesophagus, gallbladder and endometrium.

Supplements are not the answer
Results of studies that show a protective effect of foods containing certain nutrients should not be taken to mean that these nutrients, when isolated and taken as supplements, will provide the same benefits for cancer prevention. In some cases, there has been an increased risk of cancer in those people who take nutrient supplements at doses higher than the amount of that nutrient normally eaten in foods.

Suspect foods examined
While a high energy, low fibre diet may increase a person’s risk of developing cancer, some individual foods have also been singled out as potentially causing cancer (carcinogenic). These include:

• Artificial sweeteners – such as aspartame, saccharin and cyclamate. Laboratory rats can develop bladder cancer if fed huge amounts of saccharin or cyclamate, although this is at levels thousands of times greater than a normal diet. International studies agree that humans aren’t affected in the same way. Artificial sweeteners are considered safe to eat.

• Cured, pickled or salty foods – there is no conclusive evidence that red meat causes cancer. However, bacon and other cured or pickled meats contain a substance called nitrate, which has the potential to cause cancer in laboratory animals when eaten in huge doses. How this research relates to humans isn’t clear. To be on the safe side, it is best to limit the amount of cured meats in the diet because they are generally high in fat and salt. Salt has also been associated with an increased risk of stomach cancer and should be consumed in limited amounts.

• Burnt or barbecued foods – a group of carcinogenic substances called polycyclic aromatic hydrocarbons (PAHs) can be produced if foods are overheated or burnt. Although charred or smoked foods could contain traces of PAHs, experts agree that the amount in the average UK diet is too low to be considered a significant cancer risk. However, when cooking, it’s best to use relatively low temperature methods wherever possible. These include steaming, boiling, poaching, stewing, casseroling, braising, baking, stir-frying, microwaving or roasting. Avoiding char-grilled meats and foods would also be smart.

• Peanuts – some laboratory animals can develop cancer after eating peanuts that are contaminated with toxin-producing moulds. However, peanuts sold in the UK are generally uncontaminated and contamination is routinely screened for.

• Alcohol – consuming alcohol increases the risk of cancers of the mouth, pharynx, larynx, oesophagus, breast and liver. The risk is even greater in those people who smoke. Alcohol has also been associated with colon, breast and rectal cancers. Men should drink less than two standard drinks a day and women less than one standard drink a day.

Treating cancer with food
While food plays an important role in preventing some cancers, the therapeutic value of food in treating existing cancer is less clear. It is true that a person with cancer needs excellent nutrition in order to better cope with the physical demands of the illness and the rigours of medical treatment. However, claims that particular foods, vitamins or micro nutrients can kill cancer cells should be viewed with scepticism To date, there is little scientific proof that a particular food or supplement can cure cancer or destroy cancer cells.

Recently some Japanese studies have found that green tea may delay the development and spread of certain cancers. Other studies have suggested that soy may also have a similar effect. Although this work is preliminary, it may suggest a more important role for food in the treatment of cancer in the future.

Nutrition for the person with cancer is important for many reasons, including:

• The immune system needs bolstering to fight at full strength.

• The diet may be adjusted to cope with various symptoms, such as constipation, diarrhoea or nausea.

• Loss of appetite or an increased metabolism means that high energy foods may need to be included in the daily diet.

• Extra protein may be needed to help prevent loss of muscle from weight loss.

Things to remember

• High fat, low fibre diets may increase the risk of many cancers, including bowel, lung, prostate and uterine cancers.

• You can reduce your risk of developing cancer by eating more fresh fruits, leafy green vegetables and wholegrain foods.

• Even though diet can influence your risk of developing cancer, there is little evidence that special foods can be used to cure existing cancers.