SHOULD FOOD INTAKE AND CIRCADIAN RHYTHM BE CONSIDERED WHEN MEASURING SERUM CALCITONIN LEVEL?

Objective: To investigate the relationship between both food intake and circadian rhythmicity and serum calcitonin in the same individuals. Methods: Eighteen healthy subjects, 10 males and 8 females, aged 22 to 24 years, were recruited. Serum calcitonin level was measured three times: at 0800 after a 9-hour overnight fast, at 0900 postprandially, and at 1700 after another 9-hour fast. The same protocol was repeated once. Results: The mean calcitonin levels (at 0800) were 3.92 pg/mL (SD, 2.5 pg/mL) on Day 1 and 3.52 pg/mL (SD, 2.1 pg/mL) on Day 2. Mean postprandial calcitonin (at 0900) was 9.46 pg/mL (SD, 8.6 pg/mL) on Day 1 and 9.91 pg/mL (SD, 6.9 pg/mL) on Day 2. Mean fasting calcitonin in the evening (at 1700) was 6.74 pg/mL (SD, 4.73 pg/mL) on Day 1 and 6.49 pg/mL (SD, 3.57 pg/mL) on Day 2. There was no significant difference in the mean calcitonin level on days 1 and 2 for any of the three time points examined. Statistically significant differences were found between postprandial and evening calcitonin levels and the fasting levels on Day 1 (P = .018 and .015, respectively) and Day 2 (P = .001 and .0009, respectively). Conclusion: These results suggest that serum calcitonin level is significantly influenced by food intake in healthy young subjects and reveal a circadian rhythm, with increased calcitonin level during the afternoon. The timing of blood sampling relative to meals should be integrated into clinical practice and research settings involving serum calcitonin measurements.