SWIMMING AND BREAST CANCER

Every three minutes a woman in the United States learns she has breast cancer. Affecting the lives of nearly 500 women each day, this relentlessly expanding wave engulfs almost 200,000 American women each year. In 1993, some 46,000 women died of the disease, and the number keeps growing.

Experts estimate that an American woman today stands a frightening 1 in 9 chance of developing breast cancer. This represents a big increase over the 1 in 20 odds of only two decades ago. It is no exaggeration to say that breast cancer has become an epidemic.

The Causes of Breast Cancer

Many medical researchers now believe that the skyrocketing increase in the rate of breast cancer is largely a result of our sedentary, high-stress life-style and our high-fat diets. That is the bad news. The good news is that these factors are within our control. You can lessen your likelihood of contracting breast cancer through regular exercise, such as swimming, and through eating a balanced diet, both of which reduce body fat. Of course no one can guarantee that if you eat right and swim every day, you won’t get breast cancer, but these two factors alone will significantly tilt the odds in your favor. What’s more, recent evidence seems to suggest that if you do contract breast cancer, your likelihood of surviving will be greatly improved if you exercise regularly and eat a healthy, balanced diet.

There are three major identifiable causes of breast cancer: (1) family history, (2) dietary fat, and (3) percent body fat. There are also minor causes: age (the older you are, the more likely you are to contract the disease); early onset of puberty; late menopause; delayed childbearing; and a previous history of cancer. In addition, many people believe that pollution and other changes in the environment have contributed to the rise in the incidence of breast cancer over the past few decades.

Let’s look at each of the major causes.

Family History

The odds of getting breast cancer are two to three times higher for a woman whose mother or sister had the disease. The risk is even higher if that relative developed cancer before menopause or had cancer in both breasts. You cannot determine who your relatives are, of course, but if you know that your genetic background places you at unusual risk, you can improve your odds of avoiding the condition by swimming on a regular basis and by the decisions you make about your diet, birth-control methods, and postmenopause hormone therapy. Likewise, you can improve your chances of detecting the condition at an early stage by performing regular, careful breast self-examinations and by following your physician’s recommendations regarding how often you have a mammogram done.

Diet

Several major epidemiological studies have singled out dietary fat as a possible culprit in breast cancer, particularly for postmenopausal women. Other studies suggest that the large number of calories typically consumed in a high-fat diet may represent the real underlying risk. In an attempt to settle the controversy, three National Cancer Institute researchers, led by biostatistician Laurence S. Freedman, reanalyzed one hundred animal experiments, in many cases pooling data from various studies before hunting for statistical trends. In an article published in Cancer Research in 1990, they concluded that fat and calories pose independent breast-cancer risks.

A study of Finnish women, described in the November 1990 issue of the American Journal of Clinical Nutrition, analyzed dietary questionnaires filled out at least twenty years before by 3,988 healthy women aged twenty to sixty-nine and found that the 54 participants who later developed breast cancer showed a “consistently higher” average percentage of fat-derived calories. Dividing the entire sample into thirds based on the proportion of fat in the women’s diets, the authors calculated that the subgroup eating the most fat had a breast-cancer risk about 70 percent higher than the subgroup eating the least. Unfortunately the study lacked any data about the exercise habits of the women.

Chapter 4 discussed how a low-fat diet with a balance between carbohydrate and protein produces hormonal effects that protect against heart disease and other deadly illnesses. It also pointed out that certain vitamins—particularly vitamin A, especially in the form of beta carotene, vitamin C, and vitamin E—may protect against cancer, including breast cancer. Recent research seems to indicate that these vitamins provide this protection by preventing cellular and genetic damage. Taken together, these data strongly suggest that a low-fat, high-fiber diet, balanced between carbohydrates and proteins and rich in fruits and vegetables, may help prevent breast cancer.

Body Fat

Some years ago researchers discovered that when Japanese women emigrated to the United States, their incidence of breast cancer increased severalfold, mirroring the rate among native-born Americans. Obviously genetic factors could not explain this alarming rise, so the researchers concluded that it was caused by the fact that the immigrants abandoned the low-fat diet they ate in Japan in favor of an American high-fat diet.

It is, however, not only the high dietary fat you eat but what becomes of it after you eat it that is responsible for increased breast-cancer risk. According to Dr. Barry Sears, obesity, or high body fat, leads to high insulin levels in the blood. In turn, this results in a decrease in the sex hormone binding factor. Therefore, the amount of free estrogen in the bloodstream is increased. It is this free estrogen that is directly associated with breast cancer.

What happens is the free estrogen searches for estrogen receptors. These receptors can be found in large numbers in the breast tissue, and they cause these cells to grow. Among the cells the free estrogen finds are potentially malignant cells. The normal cells produce prostaglandins, which counterbalance this growth; the malignant cells do not produce the prostaglandins, so they begin to reproduce unchecked. The result is breast cancer.

According to Sears, the level of body fat that is associated with a significantly increased risk of breast cancer is 35 percent. That is well above the 22 percent threshold that defines a physically fit woman and the 17 to 21 percent for female Masters swimmers of all ages. Unfortunately, 35 percent is the average figure for American women.

The idea that maintaining lifelong physical fitness can help protect against breast cancer was supported by a long-term study of former college female athletes published by Harvard epidemiologist, Rose Frisch and her colleagues in 1992. Compared with women who were nonathletes in college, the former athletes remained more active throughout their lives, had lower body-fat percentages, and were less likely to develop breast cancer.

Another study, published in 1992, in The New England Journal of Medicine, also singled out the role of body fat in the development of breast cancer. A team of researchers led by Dr. Thomas Sellers of the University of Minnesota School of Public Health reported that high levels of body fat increased the likelihood that women whose genetic background placed them at risk would develop breast cancer.

Not only does obesity increase the risk of a woman developing breast cancer but it also increases the risk of the cancer’s recurrence. In a study of women with breast cancer headed by Dr. Ruby Senie of the Centers for Disease Control, 32 percent of obese women developed cancer recurrences, compared with 19 percent of normal-weight women.

The drug Tamoxifen is most often used to treat breast cancer. It is a powerful agent that blocks the uptake of estrogen from the breast tissues. But Tamoxifen has significant noxious side effects, and the same result can be achieved before cancer has developed by keeping insulin levels down. The easiest way to do this is through regular exercise and eating a balanced diet.

All it takes is a little discipline. Given the stakes, that’s not too much to ask.