Spring snow lowers human melatonin

We set out to find out in which way seasonal changes of environmental luminosity could affect melatonin secretion in humans.

For an entire year we collected every two months nocturnal urine samples from 20 male outdoor workers who lived and worked in an area of the circumpolar region from which exact data solar irradiance and temperature were available.

Melatonin secretion rates were assessed with our melatonin-specific radioimmunoassay.

Melatonin secretion was twice as high in December as in April, 0.88 +/- 16 nmol/12 h (mean +/- SE) vs. 0.43 +/- 9 nmol/12 h, p < 0.05. Regression analyses showed that melatonin values best correlated inversely with weeks before the urine samplings were collected was associated with a ca. 50% reduction in melatonin secretion. The association with global irradiance was weaker and none existed with temperature or other environmental variables.

Light reaching the eyes via the snow or other reflecting involved in certain biological phenomena that exhibit seasonal variations such as reproductive and self-destructive behaviours.