Natural killer cells, vitamins, and other blood components of vegetarian and omnivorous men.

The study population consisted of male vegetarians (aged 28-50 years), who were recruited from the vegetarian cohort being followed by the Department of Epidemiology (German Cancer Research Center, Heidelberg, FRG), and the same number of age- and sex-matched controls from the personnel of the same center. Among the vitamins tested, only the level of carotene was significantly higher in vegetarians; the levels of vitamin A, K, and E were not elevated. Among the other blood parameters tested, only creatinine and glutamine-transferase levels were significantly lower in vegetarians. The natural cytotoxicity of peripheral blood lymphocytes was measured using a chromium-release test. Cytotoxic activity, which is expressed as lytic units, was significantly higher in vegetarians than in their omnivorous controls by a factor of 2. The total number of white blood cells, lymphocytes, and other subpopulations did not differ between vegetarians and nonvegetarians. The enhanced natural cytotoxicity may be one of the factors contributing to the lower cancer risk shown by vegetarians.