Research suggests that there is no clear link between running volume and HDL. In one study, 56 distance runners between the ages of 20 and 56 whose average HDL cholesterol level was 63 mg/dl (3.19 mmol/L) were divided into two groups: those whose mean HDL cholesterol concentration was 73 (HIGH) and those whose average level was just 53 (LOW).10 Running volume was absolutely equivalent between these two groups. Members of both groups had also been running for about the same amount of time (6 years). Therefore, total distance and time spent running could not have accounted for the HDL cholesterol disparities.
Paul Thompson, one of the principal investigators in this study, believes that it is very difficult to predict the effect training distance will have on HDL cholesterol.11 One investigation found that jogging just 11 miles (18 km) per week produced dramatic increases in HDL cholesterol in some individuals, but running 40 miles (64 km) per week had little effect on cholesterol in other athletes.12 Genetic factors may account for some of the differences in HDL cholesterol concentrations observed in runners.13
Role of Training Intensity
Scientific research has been somewhat unclear whether the intensity of running training has a specific role to play in protecting against CHD. If two runners cover 25 miles (40 km) of running per week but one runs at an average intensity of 85 percent of O2max and the other completes his or her workouts at 65 percent of O2max, the higher-intensity runner should be fitter and therefore would expect to have greater protection against heart disease. The higher-intensity runner should also expend somewhat more calories per week during training partly because of greater postexercise caloric burns associated with the faster training. As mentioned, total calories expended on a weekly basis is an inverse predictor of CHD risk.
Definitive work in this area is lacking especially among well-trained runners, but there is evidence to support the idea that intense exercise provides more protection from CHD risk compared with low-intensity work. In the Harvard Alumni Health Study,3 individuals who expended more than 400 calories per week during vigorous activity, including running and lap swimming, had a lower risk of death; individuals who burned more than 400 weekly calories during nonvigorous activities (e.g., slow walking, yard work, gardening) did not enjoy increased protection. The Harvard Study only compared vigorous with nonvigorous activities, however; it did not look at the effects of changes in intensity within specific vigorous pursuits such as running.
A Swiss study did suggest that higher-intensity running might produce greater protection against CHD than slower-paced exertion. In the Swiss research, one group of men ran three times a week for about 30 minutes per workout at an average intensity of 75 percent of O2max while a second group trained four times a week for 30 minutes per session at a work level of just 50 percent of O2max.1 The lower-intensity group ran for 30 minutes more each week than the higher-intensity runners; energy expenditures were not actually measured. After 6 months, only the members of the higher-intensity group displayed a relationship between amount of exercise and HDL cholesterol concentrations: The more running the higher-intensity individuals completed, the higher their HDL cholesterol levels. No one experienced a cardiovascular event during this research, but loftier HDL cholesterol concentrations should protect against CHD over the long run.
Decreasing the Risk of Cancer
In addition to its strong protective effect against coronary heart disease, there is also compelling evidence that regular running lowers the likelihood of certain types of cancer, including malignancies of the blood, bladder, eye, mouth, esophagus, stomach, colon, rectum, pancreas, thyroid gland, lungs, breasts, ovaries, uterus, cervix, and vagina.
The Harvard Alumni Study already mentioned in this chapter uncovered a link between exercise and the overall risk of various forms of cancer.14 In the Harvard Study, individuals who burned more than 2,000 calories per week while running, the equivalent of running about 20 weekly miles (32 km), or engaging in other vigorous activities, had a lower death rate from cancer compared with those who expended fewer than 500 calories in weekly activity. This result was not an artifact of lower rates of smoking in the more active population.
Female Runners and Cancer
Research indicates that premenopausal women who run for about 3.25 hours per week (approximately 28 minutes per day) experience a 23 percent lower risk of breast cancer compared with women whose activity levels are lower.15 Scientific studies suggest that the protective effect of running and other forms of physical activity against breast cancer are even stronger among postmenopausal women, with the drop in risk probably greater than 30 percent.16 Even women who wait until they are in their 50s to take up running or other endurance sports enjoy a 27 percent reduction in breast cancer incidence as a result of their activity as long as they exercise fairly vigorously.17
Research suggests that there are several mechanisms by which regular running could decrease the risk of breast cancer. A key factor appears to be that running maintains a beneficial level of body leanness. Leaner women tend to produce a form of estrogen that is less potent and less likely to stimulate uterine and breast cells to divide actively. Since cell division is decreased, there is less chance that a group of cells will become malignant and begin spreading through surrounding breast tissue.18
To learn more about exercise and cancer in women, Rose Frisch and her colleagues at the Harvard School of Public Health monitored 5,398 living alumnae from 10 colleges and universities whose graduating classes spanned the time period from 1925 to 1981. Active alumnae had participated in track, cross country, basketball, crew, fencing, swimming, or tennis while in college and tended to exercise regularly after college. The runners within this active group averaged about 10 miles of running (16 km) per week. In contrast, approximately half of the 5,398 females had not participated in athletics during their college days and were significantly less likely to exercise regularly after college.19
Frisch and co-workers found that the nonactive women had about twice the risk of breast cancer and 2.5 times the likelihood of cancer of the reproductive system, including cancer of the ovaries, uterus, cervix, and vagina, than the active women. Family histories of cancer were similar between the groups, so the disparate rates of cancer were quite probably the result of activity levels not genetic factors.
Frisch and her fellow scientists found that the active women had a reduced risk of cancers unrelated to the reproductive system, too. Nonactive women experienced twice the frequency of lymphoma, leukemia, myeloma, Hodgkin’s disease, and thyroid cancer than runners and other active women. One out of every 550 nonactive women suffered from cancer of the bladder, lung, eye, or mouth while very few of the active women developed such cancers. One out of 550 nonactive women contracted cancer of the digestive system (i.e., esophagus, stomach, colon, or rectum), the frequency of which was zero in the active women. Among all cancers, only the rates of melanoma and skin cancer were similar in the two groups; in no case did runners have a higher incidence of malignancy.20
Other research supports Frisch’s findings. An inquiry that monitored the health of 25,000 women workers in the state of Washington between 1972 and 1979 discovered that physically active women, including runners, had significantly lower rates of both breast and colon cancer compared with nonactive females.21
Male Runners and Prostate Cancer
Strenuous running programs tend to reduce androgen levels in male runners, and thus the maintenance of a challenging training plan over extended periods of time should decrease the risk of prostate cancer. Cancerous prostate cells tend to grow and divide more quickly when testosterone levels are high.
Research concerning the effects of running on the risk of prostate cancer has produced mixed results, however. One investigation that followed 430,000 men in the state of Washington from 1950 to 1979 found no reduction at all in the rate of prostatic cancer with increased activity.21 An analysis of 56,683 former Harvard and University of Pennsylvania students discovered that higher levels of physical activ
ity were associated with a reduced risk of colon cancer but were linked with higher rates of prostate cancer.22
The most recent evidence suggests that running and other forms of activity are connected with a lower rate of serious prostate cancer. In a prospective study carried out in Norway over a 17-year period with a cohort of 29,110 Norwegian men, the frequency and duration of exercise were inversely associated with the risk of advanced prostatic cancer. Those men who engaged in the highest category of physical exercise, including running, had a 36 percent reduction in the risk of advanced prostate cancer and a 33 percent drop in the likelihood of dying from the disease. Interestingly, there was no association between physical activity and the overall risk of prostate cancer, suggesting that running and other endurance sports do not block the initiation of prostate cancer but are associated with preventing it from becoming invasive and deadly.23
Colon Cancer
The link between running and a reduced risk of colon cancer is extremely strong; numerous studies have documented this relationship.18 Research carried out with 488,720 participants in the NIH-AARP (National Institutes of Health and the American Association of Retired Persons) Diet and Health Study who were 50 to 71 years at baseline were monitored for more than 7 years. The study found that running or engaging in other sustained exercise five times per week lowered the risk of colon cancer by about 21 percent in men and the likelihood of rectal cancer by 26 percent in men; there was a trend for exercise to decrease colon cancer risk in women as well, but it was not statistically significant.24 Low-, moderate-, and vigorous-intensity exercise provided protection for the men as long as the running or other form of exertion was carried out five or more times per week with a weekly total duration of 7 hours or greater, which is fairly high; just 8.6 minutes per day of running has been linked with a reduction in CHD risk.
Exciting recent research with laboratory rats indicates that participation in a regular running program actually changes gene expression in the mucosal inner lining of the colon, decreasing the expression of an array of genes and increasing the transcription of several others.25, 26 The betain-homocysteine methyltransferase 2 (BHMT2) gene is one of the key bits of genetic code suppressed by running. Repression of this gene is thought to contribute to a decreased risk of developing colon cancer.
Science also suggests that prolonged running may protect the colon when it is exposed to carcinogens. In a study carried out with rats that had consumed 1,2-dimethylhydrazine (DMH), a known colon cancer inducer, the animals that ran at low intensities for 120 minutes per day, 5 days per week, had significantly fewer aberrant crypt foci (i.e., clusters of cells that are the precursors to colon malignancies) after 4 weeks compared with the rats that did not run.27
The mechanisms in addition to alterations in gene expression by which running reduces the risk of colon cancer are uncertain. Bile acids are thought to be carcinogenic, and research carried out in New Zealand found that runners had lower levels of bile acids in their colons than sedentary individuals. This decrease in bile acid concentration was found to be the result of greater fiber intake by the runners: Fiber tends to dilute colon contents. Without the added fiber, bile acid concentrations would have been the same in the two groups. After adjustment for differences in fiber intake, frequency of defecation was higher in the running group.28 More frequent defecations should permit noxious chemicals, including bile acids, to pass out of the colon more quickly, thus decreasing cancer risk.
Preventing Obesity
As one would expect, running and other forms of physical activity decrease the risk of obesity, defined as Body Mass Index (BMI) >30 kg/m2.29 This effect on obesity is one mechanism by which running lowers the risk of cardiovascular disease and cancer since these conditions are strongly linked with heightened body mass. Running and other modes of sustained exercise also prevent the weight gain associated with aging to a dramatic extent compared with inactivity.30
In a recent study carried out in Thailand with nearly 75,000 adults, running and other types of physical activity were linked with a substantially reduced risk of obesity, defined by the Asian criterion of BMI >25.31 In this research, the number of weekly sessions of running and other physical exertion was inversely related to the chance of obesity, and there was about an 18 percent increase in the likelihood of obesity with every 2 hours of daily screen time, or television watching. Both men and women who ran or engaged in other exercise daily enjoyed a 33 percent reduction in the risk of obesity.
Preventing Diabetes
Controlled trial evidence also indicates that running or other moderate physical activity combined with weight loss and a balanced diet can reduce the risk of developing diabetes by 50 to 60 percent in individuals who are at risk of developing the disease.32 Several other studies have suggested that running and walking can reduce the incidence of diabetes in men and women.33-35
Research carried out by Paul Williams as part of the National Runners’ Health Study indicates that running intensity may play a particularly important role in reducing the risk of developing diabetes.36 In this inquiry, which included 25,552 male and 29,148 female participants, the men were carrying out running training at an average intensity of 3.3 meters per second (8.3 minutes per mile) and the women were running at a mean of 3.0 meters per second (9.2 minutes per mile). Williams found that each meter-per-second upgrade in training speed for men and women reduced the probability of antidiabetic medication usage by 50 percent and 75 percent, respectively.
In Williams’ work, men who trained at faster than 7 minutes per mile (1.6 km) were 67 percent less likely to use diabetic medication compared with males who trained more slowly than 10 minutes per mile. Women who trained more quickly than 8 minutes per mile were 87 percent less likely to take antidiabetes medicine compared with women who ran at 11 minutes per mile or slower during training. Williams also showed that higher running intensities were linked with lower frequencies of high blood pressure and high LDL cholesterol levels. Although Williams’ findings do not prove causality, they do suggest that antidiabetic benefits are greater in association with faster training. This linkage was present independent of training volume: Runners could not make up for the weaker protective effect of slower training paces by running for greater total distance.
How Much Running?
The amount of running necessary to achieve some health benefit is believed to be quite small. In the United States, national physical activity recommendations call for at least 30 minutes of moderate activity (e.g., walking) on most days of the week or a minimum of 20 minutes of vigorous exertion (e.g., running) three times per week. To see if such guidelines are appropriate, researchers from the Nutritional Epidemiology Branch of the Division of Cancer Epidemiology and Genetics at the National Cancer Institute recently prospectively examined physical activity and mortality among 252,925 men and women who were participating in the NIH-AARP Diet and Health Study.37
During 1,265,347 person years of follow-up, 7,900 individuals in the research died. The results indicated that exercising 30 minutes at a moderate intensity most days of the week reduced the risk of mortality by about 27 percent; exercising vigorously for 20 minutes three times per week diminished mortality by approximately 32 percent. Meeting both of these criteria (i.e., including 3 × 20 minutes of vigorous exercise within the overall framework of moderate exertion) dropped the risk of death by 46 percent. An interesting aspect of this study was the finding that engaging in exercise for less than either recommended level also conferred a smaller benefit, lowering the risk of dying by about 19 percent. It is clear that even modest amounts of running are protective against serious health problems.
Prolonging Health During Aging
Running represents an outstanding strategy for preventing long-term disability associated with aging. Contrary to popular opinion, running does not increase the risk of osteoarthritis in knee joints; in fact, running may have a protective effect against joint degeneration in both the knees and hips.38 One study tracke
d 45 serious long-distance runners and 53 nonrunning controls over nearly two decades of life. All the individuals in the research were middle-aged or older; mean age was 58, and the range was 50 to 72 years at the beginning of the investigation.39 Despite the 20 years of hard pounding experienced by these older runners, there was no increased risk of either routine or severe osteoarthritis in the running group. In another study, 28 runners who were members of a running club and 27 nonrunner controls, initial age 51 to 68 years, were monitored for 9 years. The results indicated that runners were not at higher risk for osteoarthritis and had greater bone mineral density in their lumbar vertebrae than the nonrunners.40
A study initiated by researchers from Stanford University in 1984 tracked 538 runners for 21 years; these runners were initially 50 years of age or older, and key goals of the research were to assess how running influenced the risks of disability and mortality;41 the study also included 423 healthy, nonrunning controls. Disability was assessed by means of the Health Assessment Questionnaire Disability Index (HAQ-DI), which is scored from 0 (no difficulties at all) to 3 (unable to perform).
The average HAQ-DI score increased in both runners and sedentary controls with aging, as one would expect, but it advanced to a lesser degree in runners. Runners had a 38 percent lower risk of developing a HAQ-DI score of 0.5, which represents a beginning point for disability compared with nonrunners. After 19 years, 34 percent of the controls had died compared with only 15 percent of the runners; overall, runners enjoyed a 39 percent lower chance of dying during the study period. Even as the participants in the research approached their ninth decade of life, individuals who kept running had survival and disability curves on graphical plots of either variable versus time that continued to veer away from the curves of the sedentary controls. It is clear from this Stanford research that running does not increase the risks of joint deterioration and disablement; rather, it lowers those risks while prolonging life.
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