At least one-third of cancers are preventable, and prostate cancer is one area where evidence shows prevention can work. Various factors affect men’s risk of developing prostate cancer or the growth rate of an existing cancer. This article explores these factors and what men can do to improve their odds.
The case for prevention
The clue that we can prevent prostate cancer comes from looking at incidence rates worldwide. The rate varies greatly depending on where a man lives (ranging from 92 cases per 100,000 in the US to around 40 in Europe and Australia and down to one in China) and how hard you look for it (PSA screening is unheard of in rural China). Further, it starts in young adults as a very early premalignant (“latent”) cancer, which remains undetected even with PSA screening and causes no symptoms. The risk of harbouring one of these latent prostate cancers is high: 30% for North American males in their 40s, 50% for 50-year-olds and up to 75% for those in their 70s. Something happens to make these cancers grow in certain individuals and not others. For example, if a man emigrates from a low- to a high-risk region, his individual risk of developing a “clinical cancer” rises and within about a generation matches that of the local population. This is where factors such as the environment, lifestyle and genetics come in.
Our environment
The prostate concentrates fat-soluble compounds like a sponge, so it’s no surprise that large amounts of environmental toxins end up there. Some of these compounds mimic the androgen hormones involved in prostate cancer development. Pesticides have been associated with a doubling of prostate cancer risk.
The body has ways of dealing with unwanted chemical attacks; one of these is through vitamin D. It has been shown that prostate cancer risk is generally higher in northern climates (like Canada and Scandinavia), and is inversely related to sun exposure levels. Sunlight converts vitamin D from dietary sources into its active form. So reducing sun exposure as a way of decreasing skin cancer may have an undesirable impact on the risk of prostate cancer (as well as some other cancers). Moderate sun exposure (15–20 minutes twice a week) is now recommended, with vitamin D supplements in the winter months. Although there’s still controversy about the optimum dose, many authorities recommend at least 400 IU a day (up to 2000 IU/day is considered safe).
While it had been hoped that adding high doses of (synthetic) vitamin D to chemotherapy for advanced prostate cancer would increase its effectiveness, unfortunately this hasn’t proved to be the case. The number of deaths rose in men who took the vitamin D-chemotherapy combination and should act as a warning: more isn’t always better.
Diet and lifestyle
Canadians are becoming increasingly sedentary and overweight, and we’re eating different foods than previous generations. Dietary factors appear to play a major role in the development of prostate cancer and may also be a key to prevention.
High fat intake is associated with higher testosterone levels and increased risk. A study of men on active surveillance for prostate cancer showed that following a strict vegan diet (among other lifestyle changes) decreased PSA levels. A high-fat diet also promotes obesity, which raises the risk of high-grade prostate cancers as well as of recurrence after radiation treatment or surgery. The good news is that losing weight can reduce these risks.
A recent study correlated eating cruciferous vegetables (e.g. broccoli, cauliflower, Chinese cabbage, bok choi) more than once a week, compared to once a month or less, with a 50% decrease in the risk of prostate cancer. But the evidence isn’t clear yet. A survey of over 100,000 men followed for five years showed no benefit from diets higher in vegetables and fruits.
Many studies have shown that those who consume larger amounts of lycopene-containing foods (tomatoes, watermelon, etc) are at decreased risk of prostate cancer. In a recent study that followed over 135,000 men for six years, those who started off with the highest lycopene levels had half the odds of being diagnosed with advanced prostate cancer compared to those with the lowest baseline levels.
Eating a healthy diet also cuts the risk of heart disease and colon cancer. More men with prostate cancer are dying of heart disease, so it’s important to look at the big picture!
Supplements and vitamins
Can we get the same benefits from taking a multivitamin or other supplement as by eating right? Early research was promising but unfortunately, emerging data suggest that, with some exceptions, this approach could actually be harmful. Here’s a look at some current findings.
Vitamin E/beta-carotene. In a large Finnish study, smokers who took vitamin E and beta-carotene had a decreased risk of prostate cancer. But the trial also found an 18% increased risk of lung cancer associated with the beta-carotene component — a surprising result suggesting that not all vitamins are harmless. And, according to an analysis from an ongoing trial, the beneficial effect against prostate cancer appears to apply only to men who smoke.
Selenium. The incidence of prostate cancer is high in areas with low levels of selenium, a trace element. A study of 1,300 men who took either selenium or placebo (inactive or “dummy” pill) reported a 50% reduction of prostate cancer risk in the selenium group. A large North American prevention trial (SELECT) is testing whether a vitamin E/selenium combination can reduce the risk; results are expected in about five years. Vitamin E may have some potential harm, however — in doses above 400 IU, it may increase the risk of strokes.
Multivitamins. A large study in France (the SU.VI.MAX study) showed that, overall, there was a small (12%) decreased risk of any cancer in men who took the multivitamin (the same result wasn’t found in women, possibly because men have a poorer diet). In men whose initial PSA was greater than 3 ng/mL, those in the multivitamin group had a greater chance of being diagnosed with prostate cancer than those on placebo, while for men with lower PSA levels the multivitamin seemed to have a small preventive effect. This research suggests that multivitamins may protect those without cancer, but enhance the growth of microscopic cancers that already exist.
In a recent study of 300,000 men, those who took multivitamins more than seven times a week had a 32% greater risk of developing advanced prostate cancer and a whopping 98% increased risk of related death compared with those who didn’t take multivitamins. The threat was greatest in those with a family history of cancer, or who took individual micronutrients including selenium, zinc or beta-carotene.
Zinc. Although it’s essential for life, most people get the recommended daily amount — only 11 mg — through their regular food. Supplements containing more than 150 mg zinc may be harmful, and several studies have shown that men with higher intakes have a greater risk of prostate cancer than those who consume less.
Medications
Finasteride (Proscar®) and dutasteride (Avodart®) block the conversion of testosterone into its active form in prostate cells. The large Prostate Cancer Prevention Trial (PCPT) showed that finasteride reduced the risk of prostate cancer by 25%, with some mild side effects. Those who have a strong family history of prostate cancer may want to discuss the use of this drug with their doctor. It also helps symptoms of BPH (benign enlargement of the prostate). Dutasteride is also being investigated in a prevention study, but the results aren’t yet available.
If you’re already diagnosed
Most studies exploring supplements and lifestyle interventions in men with recurrent cancer have used PSA as the marker of success or failure, rather than progression or death from cancer. In a total of eight randomized placebo-controlled trials in recurrent cancer, four were negative and four showed beneficial effects. The benefit was generally restricted to slight decreases in the rate of PSA rise, however. The exception is a small study of 54 men with metastatic cancer who had an orchiectomy (removal of the testicles): those who also took lycopene lived an average of three months longer. This result is a little surprising and needs to be verified. In view of emerging concerns about the use of multivitamins in prevention, no supplements can be confidently recommended, although lycopene appears safe with some evidence of benefit.
A word about risks and benefits
Preventing disease implies treating large numbers of people, the vast majority of whom wouldn’t become ill anyway. Since even a small risk from the treatment (magnified by all the people taking the drug or supplement) could wipe out any benefit from a reduced risk of cancer, physicians need to be cautious about recommending a prevention strategy. On the other hand, many men with prostate cancer might accept a small risk in return for a potential benefit. But common sense is still the best policy: don’t jump at the first advertisement or website that promises a cure! The UK website Bandolier offers excellent articles on treatment risks and benefits (see further reading suggestions on page 4). ov
