By Dr Justine Butler, Senior Health Researcher & Writer, Viva!
Prostate cancer is the most common cancer in men in the UK, with over 40,000 new cases diagnosed every year. It has become the third biggest cancer killer in the UK, now responsible for more deaths than breast cancer. One in eight men in the UK will get prostate cancer at some point in their lives.
Experts think that just five to 15 percent of prostate cancers are linked to inherited genes, which means that at least 85 percent are caused by environmental and lifestyle factors.
Research shows a link between obesity and prostate cancer and men who regularly exercise have a lower risk of developing the disease. Current thinking suggests that diets high in animal fats may increase the risk, in particular, the red meats beef, lamb and pork, eggs and butter, whole milk, cheese and cream, all of which contain a lot of saturated fat.
As we see with other hormone-dependent cancers, like breast cancer, the highest incidence rates are in Australia, New Zealand and Western Europe. The lowest rates are in Africa and South-Central Asia. Yet African-American men are more affected than white American men. This suggests that prostate cancer risk is influenced by dietary and lifestyle factors.
Prostate cancer rates are highest in countries that eat lots of typical Western diet foods such as meat and dairy. However, advice from the NHS on the links between diet and prostate cancer is sparse. They say that there is evidence that a diet high in calcium is linked to an increased risk and that some research has shown prostate cancer rates appear lower in men who eat foods containing certain nutrients including lycopene, found in tomatoes and other red fruit, and selenium, found in Brazil nuts. Nothing about cow's milk and dairy products.
Despite this, it is well-documented that diets high in calcium and dairy protein can increase the risk of prostate cancer. One of the earliest reports linking dairy to prostate cancer was published in the 1980s when a study of over 27,000 Californian Seventh-Day Adventists, who had completed dietary questionnaires 20 years earlier, concluded that milk consumption was linked to death from prostate cancer. Since then, many more reports have revealed an increased risk from eating dairy foods.
Researchers from Harvard Medical School found that high consumption of calcium is linked to advanced prostate cancer. It’s been suggested that calcium may increase prostate cancer risk by suppressing circulating vitamin D.
The large, well-respected European Prospective Investigation into Cancer and Nutrition (EPIC) study found that increasing your daily dairy consumption by just 35g grams – the amount of milk you might have in a mug of tea or coffee or a small matchbox size of cheese – increased the risk of prostate cancer by 32 per cent. Interestingly, the calcium from dairy products was associated with an increased risk while calcium from other foods was not.
Other studies suggest the oestrogen content of milk may be responsible – the typical Western diet being characterised by milk and meat products and containing higher levels of oestrogen than foods eaten by Asian men, who suffer much less from prostate cancer.
One study measured the hormone contents of two kinds of commercial milks, from Holstein and Jersey cows, and found that levels were markedly higher than they were 20 years ago. This was attributed to modern dairy farming methods whereby most commercial milk is taken from pregnant cows.
Another study looked at the effects of ‘persistent milk consumption beyond weaning’ – that is adults drinking milk. They described how bioactive molecules in cow’s milk initiate signalling pathways. This, they said, combined with constant exposure to cow’s milk oestrogens from pregnant cows, may explain the links between dairy and prostate cancer.
Many studies suggest the growth factor IGF-1 may be responsible for increasing the risk of prostate cancer in dairy consumers. In one Swedish study, levels of IGF-1 were measured in blood samples from over 800 men, 281 of whom were later diagnosed with prostate cancer. Results show that those with prostate cancer had higher levels of IGF-1.
A pooled analysis of worldwide data based on 3,700 men with prostate cancer and 5,200 controls, concluded that high circulating IGF-1 levels are linked to an increased risk for prostate cancer.
Another EPIC study based on 630 cases and age-matched controls, also found an increased prostate cancer risk for men with the highest IGF-1 levels. In an extension of this work, based on 1,542 prostate cancer cases matched to controls, IGF-1 was again significantly associated with an increased risk. It was concluded that these results suggest that blood concentrations of IGF-1 in middle to late adulthood are strongly associated with subsequent prostate cancer risk.
Professor T. Colin Campbell, Jacob Gould Schurman Professor Emeritus of Nutritional Biochemistry at Cornell University, says that IGF-1 may turn out to be a predictor of certain cancers in the same way that cholesterol is a predictor of heart disease.
Dairy products increase the level of IGF-1 in the blood. In a group of healthy, middle-aged men, dairy products, milk and calcium were all associated with raised IGF-1 levels. On the other hand, high intakes of vegetables and tomatoes, or tomato-containing products, have been shown to lower levels of IGF-1.
A study published in the British Journal of Cancer noted that vegan men had a nine per cent lower IGF-1 levels than meat-eaters and vegetarians. So, again it shows that milk increases IGF-1 levels and raised IGF-1 is linked to an increased risk of cancer.
Studies consistently show strong links between IGF-1 levels and the risk of prostate cancer. Those with higher IGF-1 appear to have a significantly increased risk of subsequently developing prostate cancer, even years later.
Perhaps of greater significance, though, is the fact that recent evidence suggests that the association with IGF-1 is not so much about initiating cancer but rather how it might increase disease progression. In other words, many men develop prostate cancer or benign tumours and IGF-1 may transform these tumours into a more aggressive form of cancer. Either way, IGF-1, from cow’s milk, appears to be a risk factor that could easily be avoided by eliminating dairy foods from the diet.
Men with prostate cancer who increase their consumption of plant foods – and avoid dairy products and meat – may significantly improve their chances of survival. Researchers from the Physicians Committee for Responsible Medicine (PCRM) reviewed 25 studies and found that a plant-based diet may slow the progression of prostate cancer progression and improve the outcome.
They found that diets high in saturated fat were linked to a threefold higher risk of cancer progression and death, compared with a diet low in saturated fat. They also found that specific plant foods, including flaxseeds and lycopene-rich tomatoes, may help slow prostate cancer progression.
While the actual mechanisms underlying the development of prostate cancer are still being teased out, the effects of changing the diet have produced positive results. Researchers at the Preventative Medicine Research Institute in California evaluated the effects of dietary changes in 93 volunteers who had chosen not to undergo conventional treatment for early prostate cancer. This was a unique opportunity to observe the effects of diet and lifestyle changes without the confounding effects of radiation or surgery.
Those in the ‘lifestyle-change’ group were placed on a vegan diet rich in fruits, vegetables, whole grains and pulses with soya, vitamins and minerals. Two standard tests were used to assess their disease status. None of the vegan patients underwent conventional treatment during the study. However, six control patients decided to undergo treatment due to an increase in progression of their disease. Test results showed a favourable response in the vegan group – the magnitude of change was relatively modest but the direction of change was seen as important. It was concluded that lifestyle changes may affect the progression of early, low-grade prostate cancer. In other words, going vegan may slow prostate cancer in men who already have the disease.
In the late 1980s, eating plenty of beans, lentils, peas, tomatoes, raisins, dates and other dried fruit was found to be linked to a significantly decreased risk of prostate cancer. A decade later, a study of over 47,000 men confirmed that high levels of fructose (found in fruit) also offers some protection against prostate cancer.
More recently, it was found that while meat and dairy are linked to an increased risk, tomato products – which contain the antioxidant lycopene – vitamin E and selenium supplements have all been shown to reduce the risk. Tomato ketchup is a source of lycopene and organic brands may contain up to three times more than non-organic. A high level of physical activity was also identified as a factor in decreasing the risk of prostate cancer.
Studies have shown that soya foods may also be linked to a reduction in cancer risk. In a review of 24 studies on soya and isoflavones (the plant hormones in soya foods), results found that soya foods are linked to a reduced prostate cancer risk.
In summary, the data linking the consumption of cow’s milk and dairy products to numerous different types of cancer provides a convincing argument for eliminating all animal foods from the diet while increasing your intake of whole grains, pulses (including soya), fruit and vegetables and taking regular exercise.
Normally, only infants consume milk up until weaning and that is what every other mammal on the planet does, apart from humans. Scientists have suggested that the persistent consumption of cow's milk may provide a unique combination of factors that can lead to prostate cancer. It is a highly unusual practice – adult humans drinking breast milk from another species.
Cow's milk is a perfect food for a rapidly growing calf but that doesn’t mean it is good for human babies – or adults! If you want to improve your health by making just one change to your diet, Viva!Health recommends you ditch dairy.
Viva!Health is a part of the vegan charity Viva!. We monitor scientific research linking diet to health and provide accurate information on which you can make informed choices about the food you eat.
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