Lack of Sleep and Disease: 6 Conditions Linked to Poor Sleep

Regularly sleeping too little has been linked in research to six serious conditions: Alzheimer's-related brain changes, insulin resistance and type 2 diabetes, heart attack and stroke, a higher suicide risk in later life, ulcerative colitis and prostate cancer. Most of these findings are associations from observational studies, so they show that poor sleep and disease tend to travel together, not that one night of bad sleep causes illness. Still, the pattern is consistent enough that the US Centers for Disease Control and Prevention (CDC) recommends at least seven hours a night for adults aged 18 to 60.

Here is what six widely reported studies actually measured, what they found, and where their limits lie.

Why the body needs sleep

Sleep is not simply switching off. During the night the brain sorts and stores what you learned during the day, hormones that control appetite, blood sugar and stress follow a daily rhythm, and the body carries out repair work. When sleep is cut short again and again, these systems are disturbed.

The effects most people notice are short term: irritability, poor concentration and slower reactions, which is why drowsy driving is so dangerous. The research below looks at the longer game, asking whether people who sleep badly for years are more likely to develop chronic disease.

Keep in mind that sleep problems can also be an early symptom of illness, not only a cause. Pain, depression, heart failure and many other conditions disturb sleep, which makes cause and effect hard to separate.

Alzheimer's disease and amyloid in the brain

In October 2013, a team led by Adam Spira of the Johns Hopkins Bloomberg School of Public Health published a study in JAMA Neurology on 70 older adults from the Baltimore Longitudinal Study of Aging. Participants were aged 53 to 91, with an average age of 76.

The volunteers described their own sleep, and researchers measured beta-amyloid, a protein that builds up in plaques in Alzheimer's disease, with PET brain scans. People who reported shorter sleep had more amyloid across the brain, and those who rated their sleep as poorer had more amyloid in a region called the precuneus.

The study was a single snapshot and relied on self-reported sleep. The authors themselves said it could not prove that poor sleep causes Alzheimer's, and called for studies with objective sleep measurements. Amyloid build-up is a hallmark of the disease, but not everyone with amyloid develops dementia.

Insulin resistance, weight and type 2 diabetes

A small but carefully controlled experiment at the University of Chicago, led by Josiane Broussard and published in Diabetologia in 2015, looked at how short sleep affects metabolism. Nineteen healthy men aged 18 to 30 each spent four nights with 8.5 hours in bed and, in a separate stay at least four weeks apart, four nights with only 4.5 hours in bed.

After the short nights, free fatty acids in the blood were 15 to 30% higher from roughly 4 a.m. to 9 a.m. Insulin's ability to control blood sugar fell by about 23%, a state of insulin resistance. Broussard said the men's insulin response resembled what doctors usually see in the early stages of diabetes. The researchers also found that growth hormone and noradrenaline stayed raised during the night, which helped explain the extra fatty acids.

Because the men were young and healthy, and the experiment lasted days rather than years, it does not show that short sleep alone causes diabetes. It does offer a plausible mechanism for the link seen in large population studies, and the CDC lists type 2 diabetes among the conditions associated with insufficient sleep.

Heart attack and stroke

In 2015, researchers led by Valery Gafarov presented findings at EuroHeartCare, a European Society of Cardiology meeting, from a long-running study of 657 men in Novosibirsk, Russia, aged 25 to 64 at the start. Over 14 years, almost two-thirds of the men who had a heart attack also reported a sleep disorder.

Men with sleep problems had about 2.6 times the risk of myocardial infarction (heart attack) and 1.5 to 4 times the risk of stroke, compared with men who slept well. These figures came from a conference presentation rather than a full peer-reviewed paper, so they should be read with some caution.

The wider evidence points the same way. The CDC lists heart disease, high blood pressure and stroke among the conditions linked to too little sleep, and untreated sleep apnoea, where breathing repeatedly stops during the night, is a recognised risk factor for heart problems.

Suicide risk in older adults

A study led by Rebecca Bernert, then at Stanford University School of Medicine, was published in JAMA Psychiatry in August 2014. It drew on a 10-year study of more than 14,000 adults aged 65 and older. Researchers compared 20 people who died by suicide with 400 similar people who did not.

Those who reported poor sleep quality were about 1.4 times more likely to die by suicide over the decade. Poor sleep predicted risk better than depressive symptoms alone, and the combination of poor sleep and low mood was the strongest warning sign. Most of those who died were white men, a group already known to face higher risk, so the authors noted that more research was needed in women, minority groups and younger people.

Bernert pointed out that sleep problems are highly treatable and often less stigmatising to talk about than other risk factors. That makes sleep a useful opening for a conversation with a doctor.

If you are struggling with thoughts of suicide, help is available. In the United States you can call or text 988, and elsewhere a local crisis line or emergency service can help.

Ulcerative colitis

Ulcerative colitis is an inflammatory bowel disease that causes ulcers and inflammation in the lining of the large intestine. In 2014, Ashwin Ananthakrishnan and colleagues at Massachusetts General Hospital examined sleep and later disease among women in the Nurses' Health Study I (started 1976) and II (started 1989).

Women who reported six hours or less of sleep a night had a higher risk of developing ulcerative colitis, and so, interestingly, did those sleeping more than nine hours. The link held after accounting for factors such as age, weight and smoking. Ananthakrishnan noted that both short and long sleep have important health implications, and suggested ulcerative colitis might join that list.

The study did not find the same clear link for Crohn's disease, and because all participants were women, the results may not apply to men.

Prostate cancer

A 2013 study in Cancer Epidemiology, Biomarkers & Prevention, led by Lara Sigurdardottir, followed 2,102 older Icelandic men from the AGES-Reykjavik cohort, recruited between 2002 and 2006 and followed until the end of 2009. During that time, 135 of them were diagnosed with prostate cancer.

Men who reported trouble falling asleep had about 1.7 times the risk, and those who had trouble staying asleep about 2.1 times the risk, of men without sleep problems. For advanced prostate cancer, the hazard ratio for trouble staying asleep was 3.2, although the small number of cases made that estimate very uncertain.

One theory involves melatonin, the night-time hormone that is suppressed by light at night and that has shown anti-tumour effects in laboratory studies. The authors themselves called for larger studies with longer follow-up before drawing firm conclusions.

Association or cause, and what you can do

None of these studies proves that poor sleep on its own causes disease. People who sleep badly often also have stress, pain, shift work, depression or health problems that are hard to fully adjust for. Some results came from small groups, single scans or conference talks. What they do show, taken together, is that long-term sleep loss keeps turning up alongside conditions that affect the brain, heart, metabolism and gut.

The CDC suggests a few practical habits for better sleep:

• Go to bed and get up at the same time every day, including weekends.
• Keep the bedroom quiet, dark, calm and cool.
• Put phones and other screens away at least 30 minutes before bed.
• Avoid large meals and alcohol close to bedtime, and limit caffeine in the afternoon and evening.
• Be physically active during the day.

If you snore loudly, stop breathing in your sleep, wake up unrefreshed, or struggle with insomnia for weeks, talk to a doctor. Sleep apnoea, insomnia and restless legs are common and treatable, and treating them may matter for far more than how you feel the next morning.

Sources: Johns Hopkins Bloomberg School of Public Health on Spira et al. (2013); Spira et al., JAMA Neurology (2013), abstract; UChicago Medicine on Broussard et al. (2015); Neuroscience News on Bernert et al., JAMA Psychiatry (2014); HealthDay on Ananthakrishnan et al. (2014); Sigurdardottir et al., Cancer Epidemiol Biomarkers Prev (2013), abstract; CDC: About Sleep. Originally reported by Medical Daily, via Idealist4ever.

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