Longitudinal trends of hemoglobin levels in a Japanese population--RERF's Adult Health Study subjects.

Conflicting results have been reported on the long-term relationship between hemoglobin (Hb) level and age. We analyzed that relationship over a 40-yr period in a Japanese population, adjusting for the effects of sex, birth cohort, smoking, and anemia-associated diseases. We used Hb levels measured biennially between 1958 and 1998 for 4858 Adult Health Study subjects of the Radiation Effects Research Foundation. Using the mixed-effects model, we showed that the aging Hb profile varied by sex (P < 0.001) and birth cohort (P < 0.001). Male Hb levels peaked in the third and fourth decades and then decreased while female Hb levels dipped slightly in the third decade, peaked in the sixth and seventh, and then decreased. Levels were higher in younger cohorts. The rate of Hb decline after the sixth decade of life was greater for subjects with anemia-associated diseases (P = 0.002). The annual rate of decline between 70 and 80 yr of age for disease-free men ranged from 0.083 to 0.042 g/dL and for disease-free women from 0.049 to 0.036 g/dL. Levels were higher for ever-smokers (P < 0.001), more so for women than men. A decreasing trend in Hb concentration with advancing age was detected for elderly men and women after controlling for anemia-associated diseases, suggesting that anemia in the elderly is due not only to disease but also to aging. Cohort and smoking effects on Hb levels were also observed.