Abstract
Tryptophan is an indispensable amino acid which serves as a precursor for the neurotransmitter serotonin and other molecules of functional significance including niacin and melatonin; and is believed to participate in regulation of circadian rhythms. Intake of tryptophan, and its relationships with behavioral and sleep outcomes was examined in a representative sample of US adult population (N = 29,687; age 19 years and older) using the National Health and Nutrition Examination Survey (NHANES) 2001–2012. Tryptophan intakes were estimated by obtaining amino acid data from the USDA National Nutrient Database for Standard Reference data files. Individual usual intake (habitual intake) of tryptophan was determined using the National Cancer Institute method for estimating intake of a single dietary component. Sleep and depression related outcomes were assessed using questionnaires. For depression, a nine‐item validated screening instrument assessing symptoms of depression, the Patient Health Questionnaire (PHQ–9), was administered. Data were adjusted for demographic factors and protein intake, and P‐value for trend (P < 0.05) was determined across deciles of intake. Mean individual usual intake of tryptophan was 826 ± 3 mg/d (977 ± 6 mg/d for male and 679 ± 4 mg/d for female) among US adults (age 19 years and older); several fold higher than the Estimated Average Requirement (EAR) of 4 mg/kg/d for adults (~280 mg/d for a 70 kg adult). Usual intake of tryptophan was inversely associated with self‐reported level of depression measured by raw PHQ‐9 score (0–27; β = −0.099; P = 0.0017) and by computed level (1=no depression; 5=severe depression; β = −0.018; P = 0.0029). Tryptophan intake was positively associated with self‐reported sleep duration (β = 0.024; P=0.0184). In conclusion tryptophan intake has small but significant positive effects on self‐reported level of depression and sleep in adults. Views expressed here are those of the authors and do not reflect official policy of the US Army, Department of Defense, or US Government.Support or Funding InformationDoD/MRMC
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