Estimating dim light melatonin onset time in children using delta changes in melatonin

We aimed to establish a method for estimating dim light melatonin onset (DLMO) using mathematical slopes calculated from melatonin concentrations at three sampling points before and after sleep in children. The saliva of 30 children (mean age ± SD: 10.2 ± 1.3 years old) was collected under dim-light conditions up to six times every hour starting at 17:30 (t17), namely, 18:30 (t18), 19:30 (t19), 20:30 (t20), 21:30 (t21), 22:30 (t22), and 23:30 (t23), in the evening, and at 6:00 (t30) the following morning. We calculated SLOPE_on (mathematical slope between melatonin concentrations at t18 and t20, t21 or t22), SLOPE_off (the slope between t20, t21 or t22, and t30), and Δ SLOPE , which is generated by subtracting SLOPE_on from SLOPE_off . DLMO was estimated by multiple regression analysis with the leave-one-out cross-validation (LOOCV) method using SLOPE_on and SLOPE_off , and Δ SLOPE . The intraclass correlation coefficient (ICC) between the estimated and measured DLMOs was used as the index of estimation accuracy. DLMOs estimated using multiple regression equations with SLOPE_on and SLOPE_off yielded significant ICCs for the measured DLMOs, with the largest ICC at t20 (ICC = 0.634). Additionally, the ICC between the estimated and measured DLMOs using the equation with Δ SLOPE was significant, with a larger ICC at t20 (ICC = 0.726) than that of the equation with SLOPE_on and SLOPE_off . Our results showed that DLMO could be estimated with a certain level of accuracy from salivary melatonin levels at three time points before and after sleep in children.