Review published in Advances in Nutrition finds “a positive relation between dairy product consumption and sleep quality,” but evidence is limited.

Poor sleep quality, defined as having trouble falling and staying asleep, needing medication to sleep, or having difficulty staying awake during the day, is a risk factor for the development of various cardiometabolic diseases, including obesity and cardiovascular disease.  Emerging research suggests that for some people changes in diet could improve sleep quality.  In particular, dairy products may hold a key to better sleep quality.

Dairy products are notably rich in tryptophan, a key compound needed for serotonin and melatonin production, which in turn are instrumental for facilitating our bodies’ ability to fall asleep and stay asleep.  In addition, dairy products provide a range of micronutrients that are needed for the synthesis of melatonin, which could also contribute to their sleep-promoting effects.  Despite some promising research, however, the strength of the relationship between dairy consumption and sleep quality remains unclear.

In response, the authors of Exploring the Role of Dairy Products in Sleep Quality: From Population Studies to Mechanistic Evaluations set out to determine the strength of the association between dairy consumption and sleep quality as well as to evaluate causality by examining the results of relevant epidemiological studies and clinical trials.  In addition, the authors explored the potential mechanisms by which dairy products might affect sleep quality.

According to the authors’ findings, “existing observational and experimental data are limited, yet tentatively support a positive relation between dairy product consumption and sleep quality.”  Although more clinical trials are needed to support the review’s findings, the authors believe that supplementing the diet with dairy proteins, micronutrient cofactors in melatonin synthesis, or fermented dairy products confers favorable effects on sleep quality.  This is likely achieved through two key pathways: (1) increased tryptophan availability for conversion to melatonin and (2) improvements in the gut microbiome.

Interestingly, the authors found some evidence indicating that the timing of dairy intake may also influence its effect on sleep quality.  In one study, for example, consuming a tryptophan-rich breakfast during bright-light daytime conditions led to greater overnight melatonin levels than did consuming the same breakfast under dim-light conditions.  According to the authors, “it makes sense that timing of intake could affect changes in sleep in response to dairy protein intake because absence of sunlight is the primary catalyst for melatonin production and secretion from the pineal gland.”  As more data on the effects of dairy and dairy proteins on sleep become available, the effect of timing will be an important factor to consider to ensure that recommendations maximize melatonin synthesis and, consequently, sleep quality.

“Although the available evidence points towards a beneficial role of dairy products in sleep quality,” the authors acknowledge that “several limitations preclude the development of firm conclusions.”  For example, few clinical intervention studies have been conducted.  The authors therefore believe that “additional studies with larger samples are needed to confirm the causal effect of dairy products and their constituents on sleep quality and to elucidate the effect of dairy products in different participant groups such as male and female participants, younger and older adults, athletes and nonathletes, and, importantly, poor and good sleepers.”

Overall, the authors believe that “the studies appraised in this review provide preliminary evidence on which to build the research base needed to make recommendations targeting dairy product consumption to promote sleep quality.”

Images via