Exercise is good for the immune system but what about high volume, high intensity, chronic (long term) exercise? For cancer patients, a couple of things may be worth considering, but first a few things about immune cells. In a general sense, cancer is a failure of the immune system to detect and eliminate defective cells, or maybe more accurately, the ability of cancer cells to evade detection from immune cells.
Two categories of immune cells are: innate immune cells; and, adaptive immune cells. Natural Killer cells (NK cells) are a part of the innate immune system and they respond quickly to tumor formation and virally infected cells. T-cells are a part of the adaptive immune system and remember previous invaders, and cancer, and respond faster the second time to the same invader. Moderate intensity exercise and life long aerobic fitness improves aspects of both of these immune cell types. However, high volume, high intensity, long-term exercise training can have negative effects.
A study (1) followed Ironman competitors training for 6 months prior to the event and for a few weeks afterwards. The researchers found that by the end of study period the ratio of some T-cell subtypes changed to a composition that an older person is more likely to have. Naive T-cells, which are highly responsive mature T-cells, decreased, while terminally differentiated T-cells (senescent) increased. Terminally differentiated T-cells are not as ‘nimble’ as naive T-cells in responding to invaders, and the ratio between the two can change as one ages – more terminally differentiated T-cells accumulate and less naive T-cells are found. This change is thought to make the elderly more susceptible to infections. However, increasing aerobic fitness can lower the proportion of age-related senescent T-cells and increase naive T-cells, regardless of age (2), but maybe only to a point, as elite endurance athletes are known to get more upper respiratory infections and changes in immune cells are thought to play a role in this (3).
Another twist in this exercise puzzle is something called Cytomegalovirus (CMV). CMV is a common herpes virus infecting approximately 50% of American adults, and that percentage increases with age. CMV affects the exercise response of NK cells, particularly at the lactate level associated with the individual anaerobic threshold (4), which is an intensity that many endurance athletes periodically train at in order to improve performance – tempo runs for marathon runners are an example. Exercise increases the cytotoxicity (killing ability) of the NK cells but their numbers are decreased after a workout if one is positive for CMV, and a pronounced reductions in NK cells occurs when the workout was done at the anaerobic threshold (~ 4 mmoles lactate).
So what does this mean for cancer patients wanting to do a triathlon, marathon, or ultra? Right now there isn’t enough evidence to change the general American College of Sports Medicine (ACSM) guidelines of 150 minutes per week of moderate intensity exercise or 75 minutes per week of vigorous exercise. Although a recent breast cancer study (5) found that 300 minutes per week of moderate intensity exercise was best for post-menopausal breast cancer patients who were not on hormones. Surprisingly, another study found that higher levels of cardiorespiratory fitness was associated with higher risk of prostate cancer (6), the CMV status of those subjects was not reported and may not be known. Outside Magazine recently did an article (7) on the deleterious effects ultra-marathons has had on some participants. Perhaps CMV status or changes in T-cell proportions may be emerging as important markers to follow. Exercise can protect us against infection and fight tumors but that does not also mean greater amounts of exercise is better. Until more evidence is presented, the ACSM exercise recommendations, as generic as they are, appear to be about right for cancer patients, and maybe particularly for those who are CMV positive.
The impact of 6-month training preparation for an Ironman triathlon on the proportions of naïve, memory and senescent T cells in resting blood. Coagrove, C., et al. Eur J Appl Physiol (2012) 112:2989–2998.
Aerobic fitness is associated with lower proportions of senescent blood T-cells in man. Spielmann, G., et al. Brain, Behavior, and Immunity 25 (2011) 1521–1529.
- Upper respiratory tract infections and exercise. D.C. Nieman. Thorax. 1995 Dec; 50(12): 1229–1231.
Acute exercise preferentially redeploys NK-cells with a highly-differentiated phenotype and augments cytotoxicity against lymphoma and multiple myeloma target cells. Part II: Impact of latent cytomegalovirus infection and catecholamine sensitivity. Bigley, A.B., et al. (Article in Press) Brain, Behavior, and Immunity xxx (2015) xxx–xxx.
Effects of a High vs Moderate Volume of Aerobic Exercise on Adiposity Outcomes in PostmenopausalWomen. A Randomized Clinical Trial. Friedenreich C.M., et al., JAMA Oncol. doi:10.1001/jamaoncol.2015.2239.
Midlife Cardiorespiratory Fitness, Incident Cancer, and Survival After Cancer in Men. The Cooper Center Longitudinal Study. Lakoski, S.G., et al., JAMA Oncol. 2015;1(2):231-237. doi:10.1001/jamaoncol.2015.0226.
- Running on empty. Meaghan Brown. Outside, June 12, 2015.