Mediterranean Diet Linked to Improved Sleep Quality

Batya Swift Yasgur, MA, LSW

September 18, 2018

Adherence to the Mediterranean diet (MeDi) may improve quality of sleep in older adults, new research suggests.

Investigators analyzed sleep duration and quality, as well as adherence to the MeDi, in more than 1600 adults. Results showed that in individuals aged 65 to 75 years, sleep quality was better for those who adhered to the MeDi than for those who did not, even after adjusting for possible confounding factors, including cognitive status.

The association disappeared, however, in individuals older than 75 years. No connection was found between diet and sleep duration.

"The findings of the present study show that sleep quality, rather than sleep duration, is positively associated with adherence to the Mediterranean diet in a large sample of adults aged 65 years and above," senior author Mary Yannakoulia, PhD, associate professor of nutrition and eating behavior, Department of Nutrition and Dietetics, School of Health Sciences and Education, Harokopio University, Athens, Greece, told Medscape Medical News.

"Adopting or adhering to a Mediterranean-type dietary pattern has been repeatedly shown to have multiple beneficial effects for older people, including [avoiding] cognitive decline. So, according to our findings, following such a diet would also be good for the sleep habits of older adults," Yannakoulia said.

The study was published online September 5 in Geriatrics and Gerontology International.

Synergistic, Antagonistic Effects

"Sleep curtailment and low sleep quality are common referred problems in older adults, with several parameters, including dietary factors, that may affect sleep duration and quality," Yannakoulia said.

"Previous research has focused on caloric intake, individual nutrients, or foods that may be related to sleep patterns, but still, the assessment of individual food intake does not account for their potential synergistic or antagonistic effects on sleep parameters," she added.

"Our previous research experience looking at the components and health effects of the MeDi — a holistic, whole-diet approach — motivated us to evaluate potential associations between this plant-based pattern and sleep."

Although previous research suggested that adherence to the MeDi had beneficial effects on sleep patterns in older adults, it did not take cognitive status into account.

To investigate these questions, the researchers assessed participants in the Hellenic Longitudinal Investigation of Aging and Diet study. This population-based, multidisciplinary, collaborative study was designed to estimate the prevalence and incidence of mild cognitive impairment (MCI), Alzheimer's disease, and other types of dementia in the Greek population. It also evaluated several factors that contribute to the health status of older people.

Participants were community-dwelling older adults (n = 1639; mean age, 72.7 years) who provided information about their diet and sleep patterns.

Habitual diet during the previous month was assessed using the validated, 69-question, semiquantitative food frequency questionnaire (FFQ), which was completed by each participant or, if necessary, a caregiver.

The FFQ included questions about consumption of various foods. Participants indicated the absolute frequency of consuming a predetermined amount of food using a 6-point scale. Reponses were then converted to indicate daily intakes of specific food items and were extrapolated to indicate energy intake.

The investigators used the MedDietScore, an 11-item composite score based on the FFQ-based food consumption, to evaluate adherence to the MeDi for each participant.

Participants also completed the Sleep Scale, from the Medical Outcomes Study, consisting of 12 self-reported items. Sleep quality was used as a continuous variable (ranging from 1 to 54), with higher scores indicating greater sleep dysfunction.

Covariates included age, sex, years of education, total energy intake (kcal/day), body mass index (BMI), and depression. The researchers also assessed physical activity using the Athens Physical Activity Questionnaire.

The statistical analyses used the MedDietScore either as a continuous variable or as tertiles. The first tertile (ie, lowest adherence to the MeDi) was the reference group, which was compared with the other tertiles. The last tertile represented the greatest adherence to the MeDi.

Potential Role of Melatonin?

Compared with participants with middle and high MeDi adherence, participants with lower MeDi adherence were found to be older (72.4 ± 5.6 and 72.1 ± 5.4 vs 73.4 ± 5.9 years, respectively) and to have a higher frequency of depression (20.4% and 15.3% vs 25.7%), higher BMI (28.6 ± 4.5 and 28.6 ± 4.3 vs 29.5 ± 5.0), and lower total energy intake (1985 ± 535 kcal/day and 2118 ± 509 kcal/day vs 1829 ± 519 kcal/day).

For participants with low MeDi adherence, sleep quality was worse, as indicated by higher Sleep Scale scores, than for those with middle and high MeDi adherence (18.8 ± 7.7 vs 17.6 ± 7.8 and 16.3 ± 7.2, respectively).

The positive association between MeDi adherence in the unadjusted model persisted after adjustment for age, sex, depression, years of education, BMI, level of physical activity, and total energy intake.

In both the unadjusted and adjusted models, sleep duration was not associated with MeDi adherence. The findings did not change when the researchers excluded participants with MCI.

Further analyses of the associations between MedDietScore and individual components of sleep quality revealed that adherence to the MeDi was negatively associated with trouble falling asleep and sleep disturbance and was positively associated with sleep adequacy, even after controlling for the aforementioned covariates.

The results did not change when the sample population was divided into male and female subgroups.

However, when the sample was divided into participants aged 75 years or younger and those older than 75, both unadjusted and adjusted models showed that sleep quality was positively associated with MeDi adherence only in the younger group. Sleep duration remained unrelated to MeDi adherence in both age groups.

Yannakoulia cautioned that because the study had a cross-sectional design, it could not establish causal relationships. Rather, it is "stating hypotheses for future investigations," she said.

She suggested that one possible hypothesis for the findings is that "poor sleep quality is linked to high levels in markers of inflammation and oxidation, and anti-inflammatory as well as antioxidative properties have been extensively attributed to the Mediterranean dietary pattern."

Moreover, "some foods characterizing the Mediterranean dietary pattern, such as olives, some kinds of fish, and seasonal fruits, are good sources of melatonin, a neurohormone that modulates circadian rhythms and is involved, among others, in the sleep-wake cycle by promoting sleep and subsequently enhancing sleep quality," she said.

"Compelling Evidence"

Commenting for Medscape Medical News, Tasnime Akbaraly, PhD, French Institute of Health and Medical Research and the University of Montpellier, France, said that the study adds to increasingly "compelling evidence that there is a relationship between the quality of diet and several depressive disorders and mental health."

There may be a "bidirectional association between cardiometabolic disorders and sleep disorders," suggested Akbaraly, who was not involved with the study.

She added that, although more evidence is needed to assess whether diet directly affects sleep disorders, "the strong evidence already linking diet to cardiovascular diseases and depressive disorders — two conditions closely related to sleep problems — should lead clinicians to implement dietary habit assessments and dietary counseling during medication consultation, especially given the social and economic costs associated with unhealthy diets."

Also commenting on the findings for Medscape Medical News, Marie-Pierre St-Onge, PhD, associate professor of nutritional medicine and center director of the American Heart Association's Go Red Research Network, said that other studies have shown a relationship between specific nutrients and sleep quality and duration, but "this study shows that overall pattern of intake is also important."

She cautioned that because this is a cross-sectional study, "we don't know if poor diet leads to poor sleep quality or the other way round," but the study does have important take-home messages for clinicians, "including dietary recommendations to sleep hygiene recommendations for healthy sleep may be useful to the patients," St-Onge said.

"We should not forget that the Mediterranean diet is part of the Mediterranean lifestyle that includes, apart from the diet per se, adequate rest, regular physical activity, and conviviality," Yannakoulia added.

The study was funded by grants from the Alzheimer's Association and the Ministry for Health and Social Solidarity (Greece) and by the ESPA-EU program Excellence Grant. The study authors, Dr Akbaraly, and Dr St-Onge have disclosed no relevant financial relationships.

Geriatr Gerontol Int. Published online September 5, 2018. Full text

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