NEW YORK (Reuters Health) - Older people who spend more time sleeping have higher cholesterol levels, and less "good" HDL cholesterol, Dutch researchers report.
People who sleep fewer than seven hours a night, as well as those who log more than eight hours may be more likely to develop heart disease, although it's not clear why, Dr. Julia F. van den Berg of Erasmus Medical Center in Rotterdam and colleagues note in the medical journal Psychosomatic Medicine.
To investigate whether cholesterol might be a factor, van den Berg and her team compared sleep duration and total cholesterol levels, as well as the ratio of total to HDL cholesterol, in 768 men and women 57 to 97 years old.
The researchers used actigraphy to measure sleep duration, which involves using a wristwatch-like device to keep track of movement and has been shown to be a more reliable gauge of sleep time than a person's own report. People wore the device for five to seven days and nights.
None of the study participants used cholesterol-lowering drugs.
Overall, van den Berg's team found, people who slept longer had higher cholesterol levels. Among people younger than 65, spending a longer time in bed accounted for most of the relationship. For people 70 and older, the relationship was largely due to the fact that people with more fragmented sleep -- and therefore less sleep time -- had lower cholesterol levels.
It's possible that people who spend more time in bed may be less active, and hence have higher cholesterol levels, the researchers note, but the link between fragmented sleep and low cholesterol is more difficult to explain; underlying illness could be a possibility.
SOURCE: Psychosomatic Medicine, November/December 2008.