US scientists found that men who were fat and unfit were more likely to have raised levels of white blood cells, a marker for inflammation in the body that is believed to raise the risk of coronary heart disease and other illnesses.
The cross-sectional study was carried out by researchers from the Pennington Biomedical Research Center in Baton Rouge, Louisiana, and colleagues from other research centres, and was published online on 17 October in the British Journal of Sports Medicine (BJSM)
Corresponding author, Dr Timothy S Church, who is John S. McIlHenny professor in Health Wisdom at Pennington Biomedical Research Center, and colleagues examined the link between fitness, BMI (body mass index), and concentrations of a subfraction of white blood cells in 452 healthy, non-smoking men.
The men were taking part in a study known as the Aerobics Center Longitudinal Study, which is examining the relation of physical activity and cardiorespiratory fitness to health in the middle and later years of life.
The subfraction of white blood cells that the researchers examined were: neutrophils, lymphocytes, monocytes, basophils, and eosinophils. Lymphocytes include the “killer” T cells that attack tumour cells and the B cells that help to identify foreign material for destruction by phagocytes. Lymphocytes account for 20 to 30 per cent of white blood cells and raised levels of these cells are a marker for chronic infection.
Church and colleagues measured the resting levels of the different white blood cells in the men, their fitness levels (by measuring the maximal METS they could sustain in a treadmill exercise test) and fatness (using BMI), and adjusted the results for age.
MET, or metabolic equivalent, is the ratio of a person’s resting rate of energy expenditure compared to their working rate. Thus a MET of 1 is resting, and a MET of 8 is a jog, and 12 is a vigorous fast run or climb. The higher the METs you work at, the more calories per minute you burn and the harder you work. Very fit people can sustain a high level of METs for longer than unfit people.
The results showed that:
- Fitness was inversely linked to all white blood cell subfraction levels.
- After further adjusting for BMI, only total white blood cells, neutrophil, and basophil levels remained significantly linked to fitness.
- BMI was directly linked with total white blood cells, lymphocyte, monocyte, and basophil levels.
- When the researchers added fitness to the above model, only monocyte levels lost significant linkage with BMI.
Church and colleagues concluded that:
“Fitness (inversely) and fatness (directly) are associated with white blood cell subfraction populations.”
According to a BBC report, Church said it was clear that inflammation played a key role in heart disease and other illnesses, but what drives inflammation in the first case is not clear.
“There is nothing worse than a risk factor that an individual cannot modify, but here are two risk factors – obesity and fitness – which they can do something about,” said Church.
“Association of White Blood Cell Subfraction Concentration with Fitness and Fatness.”
Neil M. Johannsen, Elisa L. Priest, Vishwa D. Dixit, Conrad P. Earnest, Steven N. Blair, and Timothy S. Church.
BJSM Published Online First: 17 October 2008.
Source: Journal Abstract, BBC, scientificphysic.com, University of South Carolina Compendium of Physical Activities.
Written by: Catharine Paddock, PhD.