The effect of diet on sleep: new research

Good health depends on proper 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 getting enough physical activity is important for good sleep. So how can nutrition affect sleep?

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

Why sleep is important and how it works

Sleep gives our body the opportunity to rest and recover from wakefulness. Our heart, blood vessels, muscles, cells, immune system, cognitive and memory abilities depend on regular, healthy sleep for optimal functioning. 

A complete sleep consists of 3-5 night cycles, each of which lasts on average from 90 to 120 minutes. In each cycle, we start in non-rapid eye movement (non-REM) sleep, then move through two increasingly deeper stages of non-REM sleep before exiting them. Our non-REM sleep becomes progressively lighter until we reach the REM phase, after which a new cycle begins or we wake up. Adults are recommended to sleep 7 to 9 hours a day.

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

In a new study, scientists decided to examine how sleep duration may affect fruit and vegetable consumption and vice versa. They also examined the role of individual chronotypes (preferences for being active at certain times of the day, such as morning or evening) on eating habits and sleep duration.

Recommended intake of fruits and vegetables for adults

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

However, research shows that adults in many countries do not meet minimum intake levels. 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 National FinHealth Survey 2017. 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 the 134-item questionnaire the composition and frequency of their usual daily meals over the past 12 months and reported their chronotypes and typical sleep duration in a 24-hour period.

From these responses, three categories of sleep duration emerged: 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; normal sleepers have 7.7 hours and long sleepers have 10.1 hours. The majority of participants (61.7%) classified themselves as intermediate chronotypes, 22.4% indicated that they were morning types, and 15.9% were 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."

Findings: Both the amount and the 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 found 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, significant mean differences were observed in berry and other fresh and canned fruit intake between normal and short sleepers. In contrast, for normal and long sleepers, the only significant difference was in apple intake."

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 in line with the results of a 2023 study in the International Journal of Behavioral Nutrition and Physical Activity, which found decreased fruit and vegetable consumption 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. The 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 aimed at subgroups of fruits and vegetables with strong associations, such as green leafy vegetables and fruit vegetables, can lead to significant changes in behavior. Additional research, especially longitudinal studies, is needed to better understand these associations and their implications for public health." health, especially in regions with similar population structures and dietary habits as Finland," they conclude.