Is aging recorded in blood Cu and Zn isotope compositions?

Recent isotopic observations of animal samples indicate body accumulation of heavy zinc and light copper throughout life. This hypothesis has never been tested for humans, but the existence of a relationship between blood isotopic composition and age could be promising for age assessment methodologies. Dietary habits can also influence the blood zinc isotope composition, being an additional source of isotopic variation. In order to reduce this putative source of variation, we selected a population living in an isolated area (Sakha Republic, Russia) where diverse foods are of limited availability. We sampled blood from 8 male and 31 female Yakut volunteers between the ages of 18 and 74. Zinc, iron and copper were purified by liquid chromatography on ion exchange resin and their stable isotope ratios were measured using multiple-collector inductively coupled plasma mass spectrometry. According to observations of animal samples, the (66)Zn/(64)Zn ratio increases with age. We also observe that the (65)Cu/(63)Cu ratio decreases with age, whereas iron isotopic compositions are unrelated to age. The copper and zinc isotope compositions of the Yakut's blood are significantly lighter and heavier, respectively, than in samples of European and Japanese populations. The Yakut is a circumpolar population in which individuals have an elevated basal metabolic rate in response to cold stress. This elevated basal metabolic rate could enhance copper and zinc isotopic fractionation by accelerating the turnover of the copper and zinc stores.