Low or high hematocrit levels are associated with increased morbidity and mortality, mediated via
anemia or thromboembolic events, respectively. It is therefore important to identify factors that influence hematocrit. Although
androgens are known to stimulate hematopoietic cells, it is unknown whether circulating
sex steroid hormones affect hematocrit. The association between serum
sex steroid hormone concentrations and hematocrit in men aged ≥ 20 years was evaluated in a cross-sectional study of 1273 men in the Third National Health and Nutrition Examination Survey (1988-1991). Outcomes were low (<10th percentile), high (>90th percentile), and mean hematocrit. Men with low free
testosterone levels had a lower hematocrit than men with normal free
testosterone levels (P = .03), although no relationship was found between total
testosterone level and hematocrit. The relationship between
sex hormone-binding globulin (SHBG) and hematocrit was complex, with both low (P < .001) and high (P = .01) SHBG levels associated with lower hematocrit in men aged ≥ 20 years and only high (P = .01) SHBG levels in men aged ≥ 50 years. The odds ratio (OR) of high vs normal hematocrit increased as total
estradiol (OR, 2.84; P trend = .04) and free
estradiol (OR, 2.23; P trend = .09) levels increased. In this nationally representative study of men,
sex steroid hormone levels, particularly low free
testosterone and high SHBG levels, were associated with lower hematocrit, and high total and free
estradiol levels were associated with high hematocrit. Thus, changes in
sex hormone levels with aging may contribute to the increased prevalence of
anemia and thromboembolic
stroke in men as they age.