Ethnic difference in nighttime melatonin can partially explain the ethnic difference in nighttime blood pressure: A study in European Americans and African Americans

Abstract

BackgroundBlood pressure (BP) follows a diurnal pattern which is regulated by circadian clock. Epidemiological studies have demonstrated that nighttime BP is a stronger predictor of cardiovascular morbidity and mortality compared to daytime BP. Ethnic differences in nighttime BP have long been documented with African Americans (AAs) having higher pressures than European Americans (EAs). Recently, lower nighttime melatonin, a neurohormone in the superachiasmatic nucleus and key regulator of the central circadian clock, has been associated with higher nighttime BP levels in EAs. However, whether or not ethnic difference exists in nighttime melatonin secretion is unknown. This study sought to test the hypothesis that AAs will have a lower nighttime melatonin secretion compared with EAs and this ethnic difference in melatonin can at least partially explain the ethnic difference in nighttime BP.MethodsA total of 150 young adults (71 AA and 79 EA; mean age: 27.7 years old; age range: 20.5–35.9 years old, 46% females) enrolled in visit 15 of the Georgia Stress and Heart study provided an overnight urine sample for the measurement of 6‐sulfatoxymelatonin, the major metabolite of melatonin. Urine melatonin excretion (UME) was calculated as the ratio between 6‐sulfatoxymelatonin concentration and creatinine concentration. Twenty‐four‐hour ambulatory BP was measured in all participants and nighttime systolic BP (SBP) was used as a major outcome of BP regulation.ResultsAfter adjustment of age, sex and body mass index, AAs had significantly lower UME (AAs vs EAs: 0.26±0.20 vs 0.34±0.33; P=0.002) and higher nighttime SBP than EAs (AAs vs EAs: 110.0±10.2 vs 107.2±8.9 mmHg; P=0.036). Lower UME rate was significantly associated with higher nighttime SBP and this relationship did not depend on ethnicity. With a tertile increase in UME, mean nighttime SBP decreased 2.6 mmHg (P‐value for trend=0.011). The ethnicity difference in nighttime SBP was significantly attenuated after adding UME into the model (P for ethnicity=0.193). Mediation testing showed that 35.5% of ethnicity difference in nighttime SBP could be explained by UME (P=0.035).ConclusionThe present study is the first to document the ethnic difference in nighttime melatonin excretion, suggesting that AAs have an impaired circadian rhythm and low melatonin secretion compared with EAs. Furthermore, the ethnic difference in nighttime melatonin can partially explain the established ethnic difference in nighttime SBP.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.