The effect of nutrition on sleep: a new study

Good health depends on good nutrition, sufficient physical activity, and adequate sleep. There is a clear relationship between these components: good nutrition provides energy for exercise, and many people argue that sufficient physical activity is important for good sleep. So how can nutrition affect sleep?

A recent study examines the link between fruit and vegetable consumption and sleep duration. The study, conducted by a team from the University of Helsinki, the National Institute for Health and Welfare of Finland, and Turku University of Applied Sciences, is published in the journal Frontiers in Nutrition.

Why Sleep Is Important and How It Works

Sleep gives our bodies the opportunity to rest and recover from being awake. Our heart, blood vessels, muscles, cells, immune system, cognitive abilities, and memory ability all depend on regular, healthy sleep to function optimally.

A full night's sleep consists of 3-5 cycles, each lasting on average 90 to 120 minutes. In each cycle, we begin in a phase of non-rapid eye movement (non-REM) sleep, then move through two increasingly deeper phases of non-REM sleep before waking up. Our non-REM sleep becomes increasingly light until we reach the REM phase, at which point a new cycle begins or we wake up. Adults are recommended to sleep between 7 and 9 hours a night.

However, recent research shows that insomnia and reduced sleep duration are becoming increasingly common among adults. Due to factors such as stress, fast food consumption and sedentary lifestyles, sleep deprivation is becoming a public health problem linked to cardiovascular disease, cognitive decline and increased overall mortality.

In the new study, the researchers set out to examine how sleep duration might influence fruit and vegetable consumption and vice versa. They also examined the role of individual chronotypes (preferences for activity at certain times of day, such as morning or evening) in dietary habits and sleep duration.

Recommended intake of fruits and vegetables for adults

The World Health Organization recommends that people consume at least 400 g of fruit and vegetables daily, while the latest recommendations from the Nordic Council of Ministers advise increasing consumption to 500-800 g of "vegetables, fruits and berries, with half of the intake coming from vegetables."

However, research shows that adults in many countries do not reach the minimum consumption level. According to a new study, only 14% of Finnish men and 22% of Finnish women consume the recommended minimum of 500 g of berries, fruits and vegetables per day.

The research team analyzed data from the 2017 National FinHealth Survey. A total of 5,043 adults aged 18 years and older (55.9% women; mean age 55 years [SD 16.0]) provided detailed responses to a 134-item questionnaire about the composition and frequency of their usual daily meals over the past 12 months and reported their chronotypes and typical 24-hour sleep duration.

Three categories of sleep duration emerged from these responses: short (less than 7 hours/day; 21%), normal (7-9 hours/day; 76.1%), and long (9+ hours/day; 2.9%). The average sleep duration for short sleepers was 6 hours; for normal sleepers, 7.7 hours; and for long sleepers, 10.1 hours. Most participants (61.7%) classified themselves as intermediate chronotypes, with 22.4% indicating that they were morning types and 15.9% evening types.

The researchers included chronotypes as a covariate in the study, noting that many studies have not accounted for them as potential confounders. However, some studies suggest that chronotypes may influence eating behaviors. The researchers state, "Research has shown that evening chronotypes are often associated with unhealthy eating behaviors, including obesity."

Results: Both quantity and specific fruits and vegetables matter

Among the notable findings: Normal sleepers showed higher fruit and vegetable consumption compared to both short and long sleepers across all fruit and vegetable subgroups. However, consumption of different types of fruits and vegetables yielded different results.

The study explains: "In the vegetable subgroup, significant differences were found in the consumption of green leafy vegetables, root vegetables and fruit vegetables (e.g. tomatoes, cucumbers) between normal and short sleepers.

"Similarly, for normal and long sleepers, significant differences were again noted for green leafy vegetables and fruit vegetables. However, other fresh and canned vegetables such as cabbage, mushrooms, onions, peas and beans showed no significant differences.

"Across fruit subgroups, a significant mean difference was observed in the consumption of berries and other fresh and canned fruits between normal and short sleepers. In contrast, for normal and long sleepers, the only significant difference was in apple consumption."

Association between fruit/vegetable intake and sleep duration categories but not chronotypes

The researchers also noted that sleep duration categories may provide little indication of expected fruit and vegetable intake levels. This is consistent with a 2023 study in the International Journal of Behavioral Nutrition and Physical Activity that found lower fruit and vegetable intake among adolescents the day after a night of short sleep.

The new study also found that chronotypes played a minimal role in the association between fruit and vegetable consumption and sleep duration. A 2023 study found no association between fruit and vegetable consumption and chronotypes.

The researchers note that overall, decreased consumption of certain fruits and vegetables is associated with long and short sleep duration. They recommend more specific work in this area to improve understanding.

"Targeted interventions targeting subgroups of fruits and vegetables with strong associations, such as green leafy vegetables and fruiting vegetables, may lead to significant behavioural changes. Additional studies, particularly longitudinal ones, are needed to better understand these associations and their public health implications, especially in regions with similar population structures and dietary habits as Finland," they conclude.