Q I had a vasectomy 19 years ago when I was 30, but I'm now beginning to worry about the prostate cancer connection. Is it really true that having a vasectomy can cause prostate cancer? If so, what can I do about preventing it? - JP, via e-mail
A The prostate cancer/vasectomy connection is one of those medical controversies that seems to rumble on interminably. Ever since vasectomies first became popular about 20 years ago, there have been scores of medical studies carried out to determine whether or not vasectomy causes prostate problems.
At first, about half the studies said yes while the other half said no.
Then, in 1993, along came two major pieces of research that seemed to resolve the issue. These were a couple of huge studies involving over 50,000 men, and backed by the prestigious Harvard Medical School in the US.
The first was what is called a 'prospective' study, which means that the data were collected as the study continued on. Over the four-year course of the study, there were around 300 new cases of prostate cancer among the men in the study. Looking at these data, there was a 66 per cent greater risk of prostate cases among the men who had undergone vasectomy (JAMA, 1993; 269: 873-7).
The second study was 'retrospective' - which means that it looked at existing medical records. In this case, the Harvard researchers compared some 15,000 men who had undergone vasectomy with 15,000 similar men who had not. The results were virtually identical to those of the first study.
In brutal statistical terms, the risk of developing prostate cancer after vasectomy jumps from seven per 1000 men per year to 11 per 1000 men per year - an increase of more than 60 per cent (JAMA, 1993; 269: 878-82). The researchers confidently concluded that there was a genuine connection between prostate cancer and vasectomy, as the odds of these two findings being chance results were thousands to one against.
But the studies soon began to be questioned. In 1994, a very large-scale Danish report on every vasectomy case in Denmark over a 12-year period (nearly 75,000 men) compared their prostate cancer risk with the rest of the Danish male population - and found no connection at all (BMJ, 1994; 309: 295-9).
This fed a controversy that was kept alive throughout the 1990s with yet more conflicting studies.
The latest study so far has come from New Zealand, a country with the highest rate of vasectomy in the world - and apparently meticulous cancer records. It compared more than 900 men with prostate cancer with about 1200 healthy men, and found no difference in prostate cancer rates (JAMA, 2002; 287: 3110-5).
So, what's the latest verdict? Recently, US epidemiologists pulled together the evidence from 22 separate studies done over the last 20 years, and came to the conclusion that there is indeed a small extra risk of prostate cancer after vasectomy. However, they're not sure whether this is a true causal connection or due to so-called 'detection bias' (Prostate Cancer Prostatic Dis, 2002; 5: 193-203). If it's the latter, it could be, for example, that prostate cancer is more readily picked up in men submitting to vasectomy because such men are more health conscious and more likely to be regularly examined by a doctor.
On the other hand, there is evidence that a vasectomy may slightly increase testosterone levels in the blood - which is important as testosterone is known to promote prostate cancer.
On balance, therefore, there may indeed be a small increase in cancer risk.
However, the scales can easily be tipped the other way by active preventative measures - and here, in contrast, there's good evidence to support lots of possible options.
First, particular foods. Heading the list of prostate cancer preventers is the humble tomato. No less than eight studies have found that tomatoes - especially when cooked, or concentrated in products such as ketchup or tomato paste - can considerably reduce prostate cancer. The largest study (again by Harvard) showed that two to four weekly servings of tomato sauce, such as on a pizza, will reduce prostate cancer risk by as much as half (Exp Biol Med [Maywood], 2002; 227: 852-9). The active ingredient in tomatoes is believed to be lycopene, the pigment that makes tomatoes red. In fact, there's encouraging new evidence that lycopene supplements (30 mg/day) will actually shrink prostate tumours after they have developed (Cancer Epidemiol Biomark Prev, 2001; 10: 861-8.)
Brassica vegetables (such as cabbage and brussels sprouts) can also reduce prostate cancer risk (Nutr Cancer, 2002; 42: 1-9), as can foods containing phytoestrogens, such as soya. The high consumption of soya foods in Japan has been linked to their very low rate of prostate cancer. The active ingredient in soya is genistein, which has been shown to inhibit the growth of prostate cancer cells in the laboratory (J Nutr, 2002; 132: 3168-71). Genistein is also found in red clover and can slow down prostate cancer growth in laboratory animals (Prost Cancer Prostat Dis, 2002; 5: 16-21). Flaxseed has been shown to reduce prostate cancer in mice (Urology, 2002; 60: 919-24).
It may also help if you cut down on dairy products, as calcium may be contributing to the problem. Studies in the US and Sweden have shown that a high consumption of dairy products increases prostate cancer risk by 50 per cent. The culprit doesn't appear to be the fat in milk but, somewhat surprisingly, the calcium. One of calcium's effects in the body is to reduce vitamin D levels, and this vitamin is one of many micronutrients known to prevent prostate cancer (Cancer Causes Control, 1998; 9: 559-66).
There's also good evidence that antioxidants, such as vitamins A, C and E, and selenium, will help protect against prostate cancer (Clin Chim Acta, 2003; 330: 57-83).
In addition, you could take an extract of saw palmetto (Serenoa repens), which is thought to counteract the hormonal imbalances that may cause prostate problems (Br J Clin Pharmacol, 1984; 18: 461-2), and has been shown to kill prostate cancer cells in the laboratory (Cell Biol Int, 2001; 25: 1117-24).
Drink green tea - often. Regular green tea drinkers have a lower risk of prostate cancer. The Chinese, for example, who consume the most green tea in the world, have the least prostate cancer (Semin Urol Oncol, 1999; 17: 70-6).
Finally, take plenty of exercise. If you have a sedentary job, walking is the best exercise for prostate cancer prevention (Cancer Causes Control, 1998; 9: 11-8).