Here is another interesting study. The benefits of physical fitness and the hazards of obesity may result in part from opposing effects on systemic inflammation. The fitter you are, the less likely you are to have systemic inflammation. The fatter you are, the more likely you are to have systemic inflammation.
Here is the abstract:
Association of White Blood Cell Subfraction Concentration with Fitness and Fatness
OBJECTIVE: To examine the association between fitness, BMI, and neutrophil, lymphocyte, monocyte, basophil, and eosinophil concentrations in apparently healthy, nonsmoking men.
DESIGN: Cross-sectional study of 452 men from the Aerobics Center Longitudinal Study examining the resting concentration of white blood cell subfractions across fitness (maximal METS during a treadmill exercise test) and fatness (BMI) categories after adjusting for age.
RESULTS: Fitness was inversely associated with all WBC subfraction concentrations. After further adjusting for BMI, only total WBC, neutrophil, and basophil concentrations remained significantly associated with fitness. BMI was directly associated with total WBC, neutrophil, lymphocyte, monocyte, and basophil concentrations and when fitness was added to the model, only monocytes lost significance.
CONCLUSION: Fitness (inversely) and fatness (directly) are associated with WBC subfraction populations.
The very useful Medpage site explains what all this means:
"These findings provide one more potential mechanism whereby higher levels of fitness and lower levels of fatness reduce the risk of [cardiovascular disease]," the authors concluded.
An elevated white-cell count is an independent predictor of coronary morbidity and mortality. The total white count comprises subfractions of neutrophils, lymphocytes, monocytes, basophils, and eosinophils, the authors noted.
Epidemiologic studies have indicated that an elevated neutrophil concentration or total granulocyte concentration may be the strongest predictor of coronary disease incidence, carotid atherosclerosis, and mortality, they continued.
In their previous study linking fatness, fitness, and total white cell count, Dr. Church and colleagues did not examine associations of fatness and fitness with white blood cell subfractions. They addressed the issue in the current study.
The analysis involved 452 men who had preventive medicine exams in 2001 as part of an epidemiologic study. The men were predominantly non-Hispanic whites, U.S. residents, and well educated. The study excluded men with a history of diabetes, stroke, heart attack, or chronic diseases, as well as smokers.
Physical examination, including drawn blood, was performed in the morning after a 24-hour fast. The examination included assessment of blood pressure, height, weight, and anthropometry. Each participant completed an extensive questionnaire related to personal and family medical history.
Investigators assessed cardiorespiratory fitness by maximal treadmill exercise test, using a modified Balke protocol. The test continued until the participant was exhausted or the physician stopped the test for medical reasons.
The men were stratified into fitness tertiles on the basis of age- and sex-specific predicted metabolic equivalents (METs) determined at the end of the treadmill test (<10.9>25.2 to ≤28.2 kg/m2, ≥28.2 kg/m2).
The participants' mean age was 51.2. BMI averaged 27.2, maximal METS 11.7, and blood pressure 124.9/84.1 mm Hg.
The age-adjusted total white-cell count and all white-cell subfractions were inversely associated with physical fitness. For example, total white-cell count averaged 5,933 for men in the lowest fitness tertile, 5,445 for men in the middle tertile, and 5,157 in the highest fitness tertile (P<0.001). Total neutrophil count ranged from 3,237 to 2,738 from the lowest to highest fitness level (P<0.001).
The same age-adjusted analyses across fatness tertiles revealed a direct association between BMI and total white-cell count and all but one the subfractions (eosinophils). The mean total white-cell count increased from 5,227 among men in the lowest BMI category to 5,876 among those in the highest (P<0.001). Neutrophil count rose from a mean of 2819 in the lowest BMI category to 3215 in the highest (P<0.001).
In a model adjusted for age and BMI or MET, fitness and fatness maintained their associations with total white cell count. However, fitness' associations with subfractions remained significant only for neutrophils and basophils. The fatness associations remained significant for neutrophils, lymphocytes, and basophils.
The authors suggested that the inverse association between fitness and neutrophils might be the key might explain the benefits of increased physical fitness with respect to atherosclerosis and cardiovascular disease. Neutrophils may inflict endothelial damage by releasing free oxygen radicals and other cytotoxic substances. Neutrophils also stimulate the release of proinflammatory leukotrienes.
"It is reasonable to hypothesize that any mechanism that reduces the availability of neutrophils may retard the atherosclerotic process," the authors said.
BMI also correlates directly with neutrophil concentrations, and weight loss has been shown to reduce levels of neutrophils and leukocytes, they added.
The study was supported by the National Institute on Aging and the Simmons Foundation