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Physical activity Vs Cancer Risk

Physical activity Vs Cancer RiskNot moving around enough increases your risk of colon and breast cancer. Inactivity may also been linked to cancers of the womb, lung and prostate. On the other hand, the good news is that being very active can probably halve your risk of cancer.

Breast Cancer

Women with low levels of physical activity and higher body mass index levels are at more than twice the risk of developing breast cancer than women who undertake approximately three metabolic equivalent hours (MET) per day, per year, of exercise, and have lower BMI levels, the researchers (at Meharry Medical College and the Vanderbilt-Ingram Cancer Center) found. A 25 kg/m2 body mass index among Western women is considered to be normal weight, while a BMI of 25 kg/m2 among Asian women is considered to be in the overweight category and was associated with an increased breast cancer risk in this study.




Among eleven human studies that took into account many of the established risk factors for breast cancer, eight reported a decrease in the risk of breast cancer in pre-menopausal, postmenopausal or all women with high levels of physical activity compared to women with low levels of activity.


Level of exercise recommended is equivalent to about 45 minutes of brisk walking or 20 minutes of vigorous exercise per day. Some studies have reported that athletes who exercised vigorously and participated in competitive sports had a lower risk of breast cancer than did non-athletes. However, others have reported that women who do not participate in competitive sports but who exercised regularly, such as three hours per week throughout their reproductive years, had a lower risk of breast cancer as compared to women who never exercised


Post-menopausal women who walk for an hour a day can cut their chance of breast cancer significantly, a study has suggested. The report, which followed 73,000 women for 17 years, found walking for at least seven hours a week lowered the risk of the disease.


There are several possible biological explanations for the influence of exercise on the development of breast cancer. Exercise may:
  • Influence age at menarche- An early age at menarche, the age at which a girl has her first menstrual period, is an established risk factor for breast cancer. Several studies have reported that girls who exercise regularly have a later age at menarche compared to inactive girls.


  • Alter the menstrual cycle- A few studies have reported that exercise may favorably alter the menstrual cycle. The alterations in the menstrual cycle caused by exercise may lead to a decrease in estrogen levels. Estrogen is a hormone necessary for reproductive development and health in women, but increased levels of estrogen over a lifetime have been associated with an increase in the risk of breast cancer. Activities that lower the level of estrogen in a woman's body may decrease her risk of developing breast cancer.


  • Decrease weight gain and overall weight- Some studies have reported that gaining weight during adulthood and being overweight as an adult are risk factors for postmenopausal breast cancer. Physical activity and exercise may help women to maintain a healthy weight and reduce their risk of breast cancer. Exercise may be particularly important to help postmenopausal women avoid weight gain.


  • Enhance the immune system- Several studies have reported that moderate exercise may enhance the immune system. A healthy immune system helps the body fight diseases such as cancer.

Endometrial Cancer

Physical activity Vs Cancer RiskIn a population-based case-control study, in-person interviews were completed among 832 incident endometrial cancer cases and 846 age-matched controls. Physical activity from exercise, household activities, and transportation was assessed in adolescence and adulthood, as was lifetime occupational activity. Women reporting exercise participation in both adolescence and adulthood were at nearly a 40% reduced risk , compared with women reporting no exercise in either life period. Postmenopausal women who initiated exercise in adulthood were also at reduced risk . Reductions in risk were also observed for common lifestyle activities, including household activity (both life periods) and walking for transportation (adulthood). Examination of the independent and combined effect of exercise and lifestyle activities revealed that women with less active lifestyles but who reported exercise were at 35% reduced risk , whereas non-exercisers with more active lifestyles were at 40% to 45% reduced risk. Relative risks associated with obesity range from 2 to 10. Some studies have concluded that upper-body and central weight confer a higher risk than peripheral body weight, even after consideration of BMI.

Findings suggest that both lifestyle activities of lower intensity (e.g., walking and doing household chores) and intentional exercise can reduce endometrial cancer risk. It has been hypothesized that physical activity modifies the risk of endometrial cancer by reducing obesity, a known risk factor for endometrial cancer or by reducing serum estrone levels


Lung Cancer

Current and former heavy smokers who increase their physical activity levels may lower their risk of getting cancer or dying from the disease according to a new study by researchers in the Public Health Sciences Division. They found that age influenced the impact of physical activity on the participants' risk of getting or dying of specifically, lung cancer. There was a 25 percent reduction in cancer deaths in the 54 to 62-year-old smokers. There was also a 16 percent reduction in the risk of getting lung cancer for this age group. It was observed that active female smokers lowered their risk of death from lung cancer by 31 percent.

Recommended physical activity is more than eight hours per week of vigorous session. Moderate activities included housework, yard work, regular walking, light repair work or carpentry and light sports. Strenuous sports, brisk walking, jogging, chopping wood and digging in the garden were among the activities classified as vigorous.


Colon Cancer

Physical activity Vs Cancer RiskMost studies show that people who exercise are at lower risk of colon cancer or precancerous changes in the colon, compared with sedentary people. Regular exercise appears to be one factor that will predictably lower the risk of colon cancer. Physical activity was associated inversely with the risk of large adenomas (>1 cm) in the distal colon (relative risk 0.57 (95% confidence interval 0.30 to 1.08)) when high and low quintiles of average weekly energy expenditure from leisure activities were compared. Much of the benefit was reported from activities of moderate intensity, such as brisk walking.

Researches support the idea that regular, moderate physical activity (at least 30 minutes per day, at least five days per week) can have a protective effect against some cancers. Physical activity helps reduce the risk for breast and prostate cancer by regulating hormone levels in the body, and reduces colon cancer risk by speeding up the digestive process and limiting the amount of time the bowel lining is exposed to harmful substances. Exercise also can reduce cancer risk by helping people maintain a healthy weight.


Consider the following opportunities to increase your activity level:


  • Get on or off the bus one stop early

  • Take the stairs instead of the elevator or escalator

  • When shopping, park the car in the far end of the parking lot

  • Avoid labor-saving devices including the remote control

  • Take a ten-minute walk break rather than a coffee break or cigarette break

  • Go dancing with your partner or with friends

  • Walk the perimeter of the mall two or three times before you begin shopping

  • Exercise during commercial breaks while watching television

  • Work in the garden or mow your lawn

  • Plan active vacations rather than driving trips




Dated 11  October 2013


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