What dietary and lifestyle changes can a GP advise a patient to make? Dr Karine Nohr looks at the evidence
A patient with a strong family history of prostate cancer comes to you and asks what he can do to reduce his risks. What do you advise?
In summary, the dietary recommendations would be to have a high intake of deeply pigmented fruits, in particular tomatoes and pomegranate, cruciferous vegetables, legumes (soy products and whole grain) and small amounts of freshly ground flax seed. He should reduce his dairy and red meat intake, choose organic poultry and increase his fish intake.
Asian countries have very low rates of prostate cancer and this may be due to the high intake of phyto-oestrogens present in soy, particularly in fermented soy such as tempeh, miso and natto.
High soy intake is associated with a lower incidence of prostate cancer. Meta-analyses have associated soy and isoflavone intake with a decreased risk of localised prostate cancer.
Recently, an association between high alpha-linolenic acid (ALA) intake and increased rate of prostate cancer has been noted. ALA is an omega-3 fatty acid and is found in rapeseed oil, flax seed, walnuts, soy bean oil, pumpkin seed oil, seaweed, algae and grasses.
ALA is generally thought to be anti-inflammatory in activity. Freshly ground flax seeds contain 40% oil (the rest containing proteins, lignans which include antioxidants and phyto-oestrogens, which have a protective effect against prostate cancer). Until there are more definitive studies of the role of flax seed in the prevention or treatment of prostate cancer, you can advise patients to have a daily couple of freshly ground tablespoons of flaxseed.
Epidemiological data of an association between calcium intake and cancer of the prostate are mixed. In the EPIC study, high intake of dairy protein was associated with a 20% increased risk of prostate cancer. Calcium from dairy products was also positively associated with risk (risk ratio 1.2), but non-dairy calcium posed no risk. A patient-centred decision, based on their personal risk of cancer of the prostate (family history, ethnicity) versus their benefit from taking supplements (osteoporosis, family history of colonic cancer) might be advised.
Early studies suggested a benefit of reduced prostatic cancer by using selenium and Vitamin E supplements. This has not been backed up by the more recent SELECT study. However, it has been postulated that the widespread availablity of PSA testing restricts the design of this type of prevention trial, as it removes the cancers from the at-risk population.
Epidemiological evidence of an association between lycopenes (the red pigment found particularly in tomatoes) consumption and a significantly reduced risk of prostate cancer, particularly with processed tomatoes (paste, sauce etc), is not backed up by all studies. Whilst further trials are awaited, it seems reasonable advice to have at least two servings of tomato sauce weekly.
Pomegranates have been shown to slow the development and progression of prostate cancer and could prove to be a valuable tool for both healthy men and those living with the disease.
Tea is a rich source of flavanoids, pharmacologically active molecules, and is one of the most promising dietary agents for the prevention and treatment of many diseases including prostate cancer. This seems to be particularly the case for green tea. The studies show conflicting results and mork work needs to be done, but, once again, it seems to be a safe recommendation.
Provocative in vitro and animal studies regarding the role of turmeric (containing the active ingredient curcumin) in the treatment and prevention of prostate cancer will no doubt lead to human trials. Tumors from curcumin-treated animals demonstrated a marked decrease in cell proliferation and increase in apoptosis. Sufficient dosing necessitates that it be taken as a supplement, not just used to flavour food.
Chronic stress may contribute to immune system deficits. Cortisone is immunosuppressant (by dampening tumour surveillance cells and by making natural killer cells less effective) and adrenalin kills lymphocytes. Addressing stress, in general, may go some way to reducing the risk of cancer, but whether this is relevant to prostate cancer remains unclear. Measuring chronic stress is replete with difficulties; we don't know how long, or at what age, or whether there are relevant potentiating/mitigating factors that might be part of the final analysis in understanding the role of stress in the development of cancer. Prostate cancer, being often not only a chronic disease, but a disease of the older man, makes examination of that link all the more difficult. Intuitively, if for no other reason than general well-being, addressing stress would seem like a useful way to proceed.
Dr Karine Nohr is a GP in Sheffield.
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