The effects of age and cigarette-smoking on blood and plasma viscosity in men.

We measured blood viscosity and its major determinants (haematocrit, plasma fibrinogen and plasma viscosity) in 90 apparently healthy men aged 16 to 80 years. Cigarette-smokers (n = 45) had higher levels of blood viscosity, haematocrit and fibrinogen (p less than 0.001) and plasma viscosity (p less than 0.025) than non-smokers (n = 45). Blood viscosity was still higher in smokers after correction to a standard haematocrit (p less than 0.02). Fibrinogen, corrected blood viscosity and plasma viscosity rose with age in both groups, but young smokers had prematurely elevated levels of these variables and less pronounced rises with age. These results show that age and cigarette-smoking must be considered in studies of blood and plasma viscosity, and provide further evidence for an association between viscosity and arterial disease.