Non-restorative or unrefreshing sleep may raise the risk of metabolic syndrome – a group of conditions that increase the risk of diabetes, coronary heart disease, stroke, and other health problems, according to new research.

“The current results may help design more effective prevention strategies for MetS [metabolic syndrome] to ensure adequate amount and quality of sleep,” the researchers note.

The study, “Nonrestorative sleep is a risk factor for metabolic syndrome in the general Japanese population,” was published in Diabetology & Metabolic Syndrome.

What is metabolic syndrome?

Metabolic syndrome is a widespread condition that affects about a third of adults in the United States. A person has metabolic syndrome if they have three or more of these conditions:

• Abdominal obesity or a waist circumference greater than 40 inches (101 cm) in men and 35 inches (89 cm) in women.
• Blood pressure greater than 130/80 mmHg.
• Fasting blood glucose greater than 5.5 mmol/l (100mg/dL)
• Blood triglyceride levels greater than 150 mg/dL (1.7 mmol/l)
• High-density lipoprotein (HDL or ‘good’) cholesterol levels less than 40 mg/dL (1 mmol/L) for men and 50 mg/dL (1.3 mmol/L) for women

Unhealthy diets, smoking, inactivity, and sleep disorders such as insomnia, short sleep duration, and sleep-disordered breathing are known risk factors for metabolic syndrome. However, it is unclear if non-restorative sleep, a subjective experience of unrefreshing sleep, also increases the risk of metabolic syndrome.

Researchers enrolled 83 224 adults (66% male) aged 35-75 years without metabolic syndrome from the Health Insurance Association in Japan. All participants completed a questionnaire about lifestyle, including a single question about non-restorative sleep. The study began in 2011-2012 and finished in 2019, so participants were followed for a maximum of eight years. Participants’ waist circumference, blood pressure, triglycerides, blood sugar and HDL cholesterol levels were monitored regularly during the follow-up.

A total of 17.480 people developed metabolic syndrome during the follow-up. Non-restorative sleep was associated with a 12% increased risk of metabolic syndrome. In addition, after assessing each component of the metabolic syndrome, non-restorative sleep was linked with a 7% higher risk of obesity, a 7% higher risk of high blood pressure and a 6% higher risk of diabetes. However, there was no link between non-restorative sleep and triglycerides or HDL cholesterol levels.   

Other studies in the United States and China have found similar links between non-restorative sleep, metabolic syndrome, and its components. And although no association was found between non-restorative sleep and blood fats (triglycerides and HDL cholesterol) in this study, a study in Finland found links between disturbed sleep, including non-restorative sleep and altered blood fats. The differences in findings may be due to various factors, including the study design and adjustments for confounding factors.

The ways non-restorative sleep may contribute to metabolic syndrome.

According to the researchers, non-restorative sleep can contribute to metabolic syndrome through processes involving leptin, inflammation and gut bacteria.

Leptin is a hormone that decreases appetite and regulates weight. Non-restorative sleep can alter its regulation such that appetite increases and energy expenditure decreases, leading to weight gain and raised blood sugar levels. Insufficient sleep can also cause the body to produce excessive amounts of inflammatory proteins, leading to inflammation linked to obesity and insulin resistance. Finally, poor sleep can increase the production of stress hormones such as cortisol and catecholamines that can weaken the gut barrier, allow harmful bacteria to enter the bloodstream, and cause inflammation.

The researchers highlighted some limitations to the study, including their inability to access other information about sleep, such as sleep duration, the use of sleep aids and symptoms of insomnia.

“The findings of this large-scale cohort study conducted among middle-aged Japanese adults suggest that NRS is positively associated with the incidence of MetS,” the researchers note.

“In clinical settings, physicians, in collaboration with sleep experts, should assess sleep status when treating MetS and its components. Then, treatment and/or assessment of NRS scores can improve MetS,” they note.

Use these tips to improve your sleep quality.

Lifestyle factors, including diet, medications, activity levels, daily routine and night-time habits, determine your sleep quality. Try these tips if you sleep poorly or want to improve your sleep quality.

1. Limit caffeine before bedtime: Caffeine reaches the highest levels in the bloodstream 30 minutes after consumption, but it takes three to seven hours before the body clears half of it. Many studies show that drinking large doses of caffeine close to bedtime can disrupt sleep, so avoid drinking caffeine in the evening (Irish et al., 2015).
2. Reduce alcohol intake:  Alcohol close to bedtime can make it easier to fall into a deep sleep, but once it is broken down after a few hours, sleep becomes light and easily disturbed. According to research, even small amounts of alcohol before bedtime can impair sleep.
3. Exercise regularly: Regular exercise during the day can make it easier to fall asleep at night. However, exercising at night can affect sleep.
4. Go to bed at the same or similar times every night.
5. Limit exposure to bright light in the evenings and turn off electronic devices at least 30 minutes before bedtime.
6. Avoid eating large meals before bedtime. If you get hungry at night, eat a light, healthy snack.
7. Avoid loud noises in your bedroom and keep it dark and at a comfortable temperature.
8. Find techniques to manage stress – relaxation, mindfulness, journaling, and meditation may help.
9. Avoid nicotine close to bedtime.

Reference

1. Irish, L.A., Kline, C.E., Gunn, H.E., Buysse, D.J., & Hall, M.H. (2015) The role of sleep hygiene in promoting public health: a review of empirical evidence. Sleep Medicine Reviews, 22: 23-36.
2. Centres for Disease Control and Prevention (2022). Tips for better sleep. Available: https://www.cdc.gov/sleep/about_sleep/sleep_hygiene.html. Accessed: 05 March 2023.
3. American Academy of Sleep Medicine (2020). Healthy sleep habits. Available: https://sleepeducation.org/healthy-sleep/healthy-sleep-habits/. Accessed: 05 March 2023.

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