The relationship of variations in children's growth rates to seasonal climatic variations.

The growth rates in stature of 300 children in the Orkney Islands, measured at monthly intervals over 2 years, were negatively correlated with various measures of light and temperature. All correlations were small but statistically significant, the highest being with the mean of the maximal daily temperatures (-0.32) for the boys and with hours of bright sunshine (-0.29) for the girls. The children's mean growth rates reached maxima at midwinter and minima at midsummer but the maximum in the winter 1971-72 was much lower than those at the beginning of 1971 and at the end of 1972. The climatic variables were not appreciably different in the two years. Only about 35 per cent of children showed cycles of growth rates which could be regarded as seasonal in that they rose to peak values at approximately the same time in the two successive years. The difference between the maximal and minimal rates exhibited by Orkney children (5.26+/-0.12 cm/yr for boys; 5.46+/-0.14 cm/yr for girls) was almost identical to that in London children. The synchronization of the maximal growth rates was no more precise in Orkney than in London. It is concluded that seasonal variations in light and temperature exert at most only a small effect on growth rate and perhaps none at all. The influence of other factors, as yet unidentified, is greater.