Although heart disease is our number one killer, many of us fear cancer the most.
More than 100 different types of cancer exist. The leading cancer killer for both men and women is lung cancer, followed by breast, prostate and bowel (colon) cancer. In the US, cancer is now the leading cause of death in young women between the ages of 25 and 44 years. About 35% of cancers are attributed to dietary factors (e.g. high fat, low fibre) and around 30% due to smoking. The American Cancer Society recommends avoiding all tobacco use and eating a low-fat, high fibre diet containing plenty of wholegrains, fruits and vegetables in order to reduce cancer risk. However, evidence is now mounting that our sedentary lifestyles may contribute significantly to the development of cancer. So much so, that in 1996, the American Cancer Society added physical activity as an important preventive measure.
That exercise may provide some protection against cancer is not new. Studies conducted in the 1920s made these observations but it is only in the last decade that medical scientists have re-opened the casebook. Since then many studies have confirmed an exercise-cancer prevention connection.
One of the most common forms of cancer in white females over 40 is breast cancer and is the leading cause of death in women between the ages of 40 and 60. Main risk factors include family history, first menstrual period at an early age, menopause at a late age, first childbirth after 30, or no childbirth and a high-fat diet. Until relatively recently, many women assumed they had no control over preventing breast cancer if they had a strong predisposition to the disease.
However, a recent study by Leslie Bernstein, professor of preventive medicine at California’s Norris Cancer Centre revealed statistics to the contrary. She found that women who had been habitually active from the time they started menstruating were 30-60% less likely to develop breast cancer by the age of 40, than non-exercisers. Furthermore, a study in Washington DC which reviewed the death records of 25,000 women, revealed that those who had worked in physically demanding jobs had significantly fewer deaths from breast cancer. Another US study on 16,000 women showed that those who took regular aerobic exercise had a 50% reduction in breast cancer risk. Norwegian scientists investigating 26,000 women found that those who were regular exercisers had overall 37% fewer breast cancers than those who were sedentary – but interestingly showed that the risk of breast cancer was 72% lower in lean women who exercised regularly compared to the non-exercisers.
Exercise can also help to lower risk of developing other female reproductive cancers. Although research is limited, there is increasing evidence to show that regular exercisers are at significantly less risk for both ovarian and uterine cancers than sedentary women.
How does exercise help lower breast cancer risk?
Medical scientists have discovered that regular moderate exercise lowers the body’s production of two ovarian hormones (oestradiol – a type of oestrogen – and progesterone) linked to breast tumour development. The body’s susceptibility to oestradiol and progesterone is greatest between ovulation and the beginning of menstruation. Regular exercise appears to postpone ovulation until later in the woman’s monthly cycle, thereby reducing the number of days her body must combat these potentially harmful hormones. In addition, regular moderate exercise burns fat, a pre-requisite for oestrogen production. So the fat which is used to manufacture unwanted amounts of oestrogen is used in fat-burning exercise.
It has also been found that in pre-pubescents, girls who exercise regularly tend to get their first periods up to several years later than sedentary girls and physically active young girls who have started menstruating may not actually ovulate until later. Reducing the number of ovulations that a woman experiences over a lifetime means less exposure to oestrogens and progesterone.
Leanness is also important, since as body fat levels increase so generally does the level of oestradiol. For this reason, many researchers feel that the reduction of body fat with regular exercise may be one of the key protective mechanisms against breast cancer.
The fortification of the body’s immune system that results from regular moderate physical activity is also thought to play a key role in lowering cancer risk. Natural Killer (NK) cells are an important part of the immune system and provide a first line of defence against various pathogens. They have the ability to inactivate viruses and have an anti-tumour action, helping prevent the metastatic growth potential of cancerous cells. Other immune system cells, known as T-cells also defend against viral and fungal infections, help destroy cancer cells and prevent tumour growth. Regular moderate exercise is known to boost the levels of both NK and T-cell activity and thus help the body defend itself against illness.
Regular exercise can also reduce levels of glucose and insulin and increase levels of corticosteroid hormones, which reduces cancer risk. Exercise increases interferon production and improves metabolism of ascorbic acid (Vitamin C) – which may both help prevent the formation cancerous tumours. Other potential effects of exercise in the prevention of cancer include beneficial changes to the body’s antioxidant functions and prostaglandin metabolism.
Numerous investigations have shown that people who have sedentary lifestyles have significantly greater risk of developing colon cancer. Of 35 studies conducted worldwide, 30 showed that physically active people have significantly less colon cancer than sedentary counterparts. Research at Harvard University on over 48,000 health workers revealed that colon cancer risk was 50% lower in people who took regular exercise compared to those who led sedentary lifestyles. Another study showed that 2 hours a week or more of moderately vigorous physical activity lowered the risk of colon cancer by 40%. It seems that improved bowel movements (peristalsis), often seen in regular exercisers, shortens the time that various cancer-producing chemicals stay in the colon. It is well reported that regular exercisers suffer less from constipation than sedentary people. So exercise has an effect on the colon rather like that of dietary fibre. In addition, obesity and inactivity lead to higher blood insulin levels (a hormone that can affect the colon-lining cells). Regular exercise promotes leanness and reduces insulin levels.
There are only about 15 studies investigating physical activity and prostate cancer and findings are mixed. However, around half of them showed that physical inactivity was a significant risk factor. A 16-year study in Norway on 53,000 men found that the risk of prostate cancer was reduced by 50% in those over-60s who walked regularly during their work and leisure-time. Research in Dallas revealed a 74% reduction in developing prostate cancer when comparing ‘low fitness-inactive’ with ‘high fitness-regularly active’ groups of men.
Research has found that physically fit, active individuals have overall, around four times less cancer than their sedentary counterparts.
So, regular moderate exercise can play a significant role in reducing your cancer risk.
Good health, good fitness – stay active.
Whilst it is generally thought that exercise does not help treat cancer once it is formed, many physicians now recommend regular exercise to cancer patients to improve fitness, life quality, self-esteem and morale.
However, the exercise should be symptom-limited, progressive and individualised. Providing there are no specific contraindications to exercise, general ambulation is generally encouraged for most sedentary and deconditioned cancer patients. Short bouts of exercise of around 5-10 minutes, including aerobic activities such as walking, coupled with exercises to improve range of joint motion, general flexibility and muscle strength are often prescribed. As the patient improves, this may be built up to more continuous exercise sessions lasting 15-20 minutes.
Whilst there is limited research on the role of exercise in cancer rehabilitation, the available data suggest a strong psychological role for regular physical activity.
One recent US study showed that breast cancer patients exercising for 30 minutes, 4 days a week showed significantly less depression scores and more self-esteem than non-exercising counterparts.
For most cancer sufferers, loss of body mass and ‘functional fitness’ are amongst the serious outcomes. The loss of ‘functional fitness’ includes difficulty in doing household jobs such as cleaning, vacuuming, washing & ironing, difficulty in walking and climbing stairs. Over 75% of cancer survivors report extreme feelings of fatigue during radiotherapy and chemotherapy, which are associated with loss of weight, loss of muscle, strength and cardiovascular endurance. Maintaining and restoring this ‘functional fitness’ are challenges for the cancer survivor – even those patients who are considered ‘cured’. Studies show that regular, moderate physical activity – a combination of aerobic and resistance exercises – can significantly assist recovery in cancer survivors. An increased level of activity will assist the patient to return to physical independence and an improving quality of life.