US researchers found that a contributory factor to hypertension in older men may be a lack of slow-wave sleep.
Slow-wave sleep is one of the deeper stages of sleep, from which it is difficult to wake, and is characterised by non-rapid eye movement.
Professor Susan Redline and colleagues at Brigham and Women's Hospital in Boston, Massachusetts, looked at whether sleep-related factors were linked to the risk of developing hypertension.
The importance of sleep to health and cardiovascular disease has become increasingly apparent in recent years, the researchers pointed out.
In particular, sleep-related factors may influence metabolism and hormonal systems and studies have shown that heart rate and BP falls during slow-wave sleep, they said.
What did the study examine?
The Boston research team looked at whether new diagnoses of hypertension were associated with sleep-disordered breathing, sleep duration or patterns of different stages of sleep ('sleep architecture').
The researchers enrolled 784 men over 65 years old who did not have hypertension when they were assessed at the beginning of the study. The men were assessed during sleep at home for sleep-disordered breathing, sleep duration or sleep architecture.
Upon follow up, an average of 3.4 years later, 234 of the men had developed hypertension.
What did the researchers find?
The team found that, after adjusting for age, ethnicity, locality and BMI, the only sleep-related factor associated with new hypertension diagnosis was the proportion of time men spent in slow-wave sleep.
The researchers calculated that the risk of developing hypertension was 83 per cent higher for those who spent the least time in slow-wave sleep (the bottom quarter) compared with those who spent the most time in slow-wave sleep (the top quarter).
The impact of having little short-wave sleep was not reduced when total sleep duration, sleep fragmentation and sleep-disordered breathing were factored into calculations, the researchers said.
What do the researchers make of the findings?
Professor Redline and her colleagues said their research added to 'the growing body of literature that associates sleep architecture with metabolic and physiological changes that may reflect altered neurohormones and inflammatory markers'.
They pointed out, however, that the lack of 24-hour ambulatory BP monitoring for hypertension may have undermined their results, though they controlled a far as possible for confounding effects linked to single BP measurements.
Professor Redline and her team said further studies would be needed to confirm their observations and to elucidate the causal pathways underlying the findings.
But they also stressed that studies would need to look at whether it would be possible to reduce men's risk of developing hypertension by lengthening the amount of time they spent in slow-wave sleep.
Are the findings significant?
Natasha Stewart, senior cardiac nurse at the British Heart Foundation, pointed out that, although the study indicated a link between lack of sleep and the development of high BP, it only looked at men aged over 65.
'We would need to see more research in other age groups and involving women to confirm this particular association, she said.
'However, we do know more generally that sleep is essential for staying healthy,' she added.
'It's important we all try to make sleep a priority and get our six to eight hours of shut- eye a night.'