NATURAL-KILLER-CELL ACTIVITY IN ELDERLY MEN IS ENHANCED BY BETA-CAROTENE SUPPLEMENTATION

Natural killer (NK) cell activity has been postulated to be an immunol ogic link between beta-carotene and cancer prevention. In a cross-sect ional, placebo-controlled, double-blind study we examined the effect o f 10-12 y of beta-carotene supplementation (50 mg on alternate days) o n NK cell activity in 59 (38 middle-aged men, 51-64 y; 21 elderly men, 65-86 y) Boston area participants in the Physicians' Health Study. No significant difference was seen in NK cell activity due to beta-carot ene supplementation in the middle-aged group. The elderly men had sign ificantly lower NK cell activity than the middle-aged men; however, th ere was no age-associated difference in NK cell activity in men supple mented with beta-carotene. beta-carotene-supplemented elderly men had significantly greater NK cell activity than elderly men receiving plac ebo. The reason for this is unknown: however, it was not due to an inc rease in the percentage of NK cells, nor to an increase in interleukin 2 (IL-2) receptor expression, nor to IL-2 production. beta-carotene m ay be acting directly on one or more of the lytic stages of NK cell cy toxicity, or on NK cell activity-enhancing cytokines other than IL-2, such as IL-12. Our results show that long-term beta-carotene supplemen tation enhances NK cell activity in elderly men, which may be benefici al for viral and tumoural surveillance.