NOCTURNAL MELATONIN LEVELS AT DIFFERENT GEOGRAPHICAL LATITUDES: A COMPARATIVE ANALYSIS WITH THE MID-LATITUDE POPULATION OF UZBEKISTAN

Abstract

This study evaluated nocturnal salivary melatonin levels in a mid-latitude population of Uzbekistan and compared the observed pattern with published data from populations living at higher and lower geographical latitudes. The study included 200 apparently healthy individuals aged 6–69 years who were divided into five age groups. Nocturnal salivary melatonin concentrations were measured by enzyme-linked immunosorbent assay under standardized low-light conditions. A pronounced age-dependent decline in melatonin levels was observed, from 150.60±5.64 pg/mL in children aged 6–12 years to 19.47±3.50 pg/mL in participants aged ≥60 years (F=192.7; p<0.001). Comparative analysis with published international data suggested that the melatonin profile of the Uzbekistan population occupies an intermediate position between patterns reported at higher and lower geographical latitudes. This observation is consistent with the known influence of photoperiod on the timing, duration, and amplitude of melatonin secretion. The findings indicate that geographical latitude, seasonal light exposure, and local photoperiodic conditions should be considered when interpreting nocturnal melatonin measurements. Region-specific reference values may therefore be more appropriate than direct application of reference ranges established in geographically distant populations.