Tuesday, December 04, 2007

Significant Changes in Sleep Pattern Can Affect Mortality Risk

The study found that decreasing nightly sleep from 6, 7, or 8 hours doubles the risk for cardiovascular death, while increasing sleep from 7 or 8 hours doubles the risk for non cardiovascular death.
"If you have a regular pattern — 6, 7, or 8 hours — and you maintain that over time, that's protective against premature mortality," said Jane E. Ferrie, PhD, a senior research fellow in department of epidemiology and public health at University College, London, in the United Kingdom, and lead author of the study.
"If you move out of that to the 9-hours-or-more category, that seems to increase all-cause mortality and the group of deaths that increases is the non  cardiovascular deaths. If you go to the short end of the spectrum, you increase your risk for cardiovascular mortality."
Changing Sleep Patterns
While other studies have looked at associations of sleep and mortality, this is the first to look at the health effects of significant changes in sleep patterns over time, Dr. Ferrie told Medscape Psychiatry.
The Whitehall II study of London-based civil servants aged 35 to 55 years began enrolling participants in 1985 with baseline (phase 1) screening continuing until early 1988. Data collection for phase 3 took place in 1992–1993. Both phases involved a clinical evaluation, including measurement of cardiovascular risk factors (body-mass index, systolic and diastolic blood pressure, total cholesterol), and self-administered questionnaires that included questions about duration of sleep. Participants in phase 1 selected from these sleep categories; 5 hours or less; 6 hours; 7 hours; 8 hours; and 9 hours or more. For phase 3, the response categories of 1 to 12 hours of sleep were collapsed to form categories identical to the initial phase.
Researchers collected data on 9781 participants at phase 1 and on 7729 in phase 3. Mortality data were available from the National Health Services central registry until September 2004, a mean of 17.1 years from phase 1 and 11.8 years from phase 3.
Double Mortality Risk
The study found a U-shaped association in both phases between sleep and subsequent all-cause mortality. It also showed that decreasing sleep from 6, 7, or 8 hours doubled the cardiovascular mortality risk (fully adjusted hazard ratio for cardiovascular disease of 2.04) and that increasing sleep from 7 or 8 hours also doubled the risk for death, but for noncardiovascular mortality (fully adjusted hazard ratio for noncardiovascular deaths of 2.06).
("Normal" sleep categories of 6, 7, and 8 hours had to be pooled because researchers did not have enough data to look at the categories separately, they note.)
The link between decreased hours of sleep and higher cardiovascular mortality risk seems to make some sense: Short sleep duration is a risk factor for weight gain, insulin resistance, and type 2 diabetes, the authors write. Short sleep is also accompanied by increased cortisol levels and abnormal growth hormone secretion and has been associated with hypertension and some cardiovascular diseases, they said. "It's fairly obvious what's going on there," Dr. Ferrie added.
Link Between Deaths and Long Sleep Unclear
However, the link between deaths and longer sleep patterns is not as clear. "At the other end of the spectrum, until we have sufficient deaths where we can see what is making up that noncardiovascular group of deaths, we can't explore that any further," said Dr. Ferrie. "We really don't know what's driving that." She did say, though, that long sleep is associated with depression and that researchers may want to take a look at the role of increased cancer deaths or trauma deaths among patients changing to a long sleep pattern.
This new research is bound to generate a lot of interest among sleep researchers, she added. "I think lot of people will look at this . . . and hopefully they will be able to elucidate what's making up those noncardiovascular deaths," said Dr. Ferrie.
A significant change in sleep patterns may be a red flag for some underlying disease, she said. "If somebody comes to you and they're now reporting having moved from a normal sleep pattern either to the very short end of the sleep spectrum or the long end of the sleep spectrum and that appears to be a pattern that's continuing over time and is not their regular pattern, then that is probably a marker of something."
Sleep experts are even discussing the merits of restricting sleep of people who regularly sleep 9 or more hours per night, she said.
Coauthor Francesco P. Cappuccio, MD, holds the Cephalon Chair, an endowed post at Warwick Medical School, in Coventry, United Kingdom, the result of a donation from the company. The appointment to the chair was made entirely independently of the company and the postholder is free to devise his own program of research. Cephalon does not have any stake in IP associated with the postholder, and the chair has complete academic independence from the company. Other authors declare no conflicts of interest.
Source: Sleep, Dec 2007