Sleep deprivation increases cardiac risk in women

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Sleep deprivation increases cardiac risk in women

Deborah Josefson Nebraska

Both chronic sleep deprivation and oversleeping increase the risk of heart disease in women, a new North American study has found (Archives of Internal Medicine 2003;163:205-9).

As short term sleep deprivation has been associated with increases in cortisol and cholesterol levels, as well as causing increases in sympathetic tone and hypertension, researchers from the Harvard School of Public Health in Massachusetts and from the Department of Medicine in Vancouver, British Columbia, sought to investigate whether chronic sleep deprivation increased the risk of heart disease in women.

Led by Drs Najib Ayas and Frank Hu, the researchers undertook a prospective cohort project involving 71 617 women enrolled in the nurses health study. The women, aged 45 to 65 years at the start of the study, had no history of heart disease at that time.

The participants completed a detailed questionnaire about sleep habits when the study started in 1986 and were followed up for 10 years. Subjects were asked to categorise the average length of time they slept in 24 hours as five hours or less, six hours, seven hours, eight hours, nine hours, 11 hours, or over 11 hours. Participants who had histories of heart disease or cancer before 1986 were excluded.

The primary end points of the study were fatal coronary heart disease and non-fatal myocardial infarctions.

Through 10 years of follow up, a total of 934 coronary events (271 fatal and 663 non-fatal) were documented. After adjusting for body mass index, smoking history, physical activity, menopausal status, use of hormone replacement therapy, alcohol consumption, aspirin use, and history of depression, the researchers found that the age adjusted relative risk for heart disease, when compared with a standard of eight hours’ sleep in 24 hours, was 1.45 (range 1.10-1.92) for women reporting five hours or less of sleep, 1.18 (0.98-1.42) for six hours or less, and 1.09 for those who slept seven hours in a 24 hour period.

The relative risk of heart disease in women sleeping nine or more hours was 1.38 (1.03-1.86).

The researchers did not adjust for a history of diabetes or hypercholesterolaemia because these illnesses have themselves been associated with sleep deprivation. In their report, the investigators stated: "Adequate daily sleep should not be considered a luxury, but an important part of a healthy lifestyle."

They admit to being perplexed by the finding that oversleeping was associated with a greater risk of heart disease but suggest that further studies be undertaken to determine if oversleeping is itself a marker for confounding illnesses such as sleep apnoea.

Only 37% of Americans get eight hours’ sleep a night, and 31% get six hours’ or less, according to a recent poll from the National Sleep Foundation in Washington, DC.

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