Seasonal variations in hair zinc concentrations in Canadian and African children

Proximal occipital scalp hair samples were collected during three survey periods from 30 omniverous Canadian boys aged 75.6 +/- 10.4 months (mean +/- SD) and 66 rural Malawian children (37 M; 29 F) aged 62 +/- 10 months (mean +/- SD) consuming predominantly plant-based diets. Hair samples were washed and then analyzed for zinc and copper using instrumental neutron activation analysis. Selected anthropometric measurements were also taken and dietary intakes calculated from weighed dietary records. A marked seasonal variation in hair zinc concentrations occurred in both groups; levels were highest in the season with shortest daylight hours (i.e. December/January in Canada vs July/August in Malawi). A similar trend was not observed for hair copper concentrations. Changes in hair zinc were not associated with changes in growth indices, age, socio-economic group, method of infant feeding, in either group, but were related to intakes of protein (per 1000 kcal) (p = 0.02, r = -0.36), zinc (mg day-1) (p = 0.01, r = -0.39), and dietary fiber (g day-1) (p = 0.04, r = 0.28), in the Malawian children during the second survey period. The seasonal effect on hair zinc concentrations must always be considered when interpreting hair zinc concentrations in children; its etiology remains unclear.