Monday February 9 2009
Obesity is a major risk factor for obstructive sleep apnoea
“People who cannot sleep at night should lose at least two stone in weight”, the Daily Express reports. The newspaper adds that scientists have said the “best treatment for a sleep disorder is to put the patient on a diet”. It says a study in patients with obstructive sleep apnoea (which causes interruptions in breathing during sleep) found those put on a diet showed marked improvements in their sleep and each lost 20 pounds (9kg).
This study provides evidence that “lifestyle modification”, which includes advice on diet and exercise, is effective at treating obstructive sleep apnoea if delivered using an intense programme. As such, people with mild obstructive sleep apnoea are advised to follow advice to exercise more and lose weight. Those with serious symptoms need a full assessment.
The Daily Express may have given the impression that all sleep disorders can be solved by weight loss. This is not the case, as not all sleep disorders are due to obstructive sleep apnoea. There are many other reasons for disturbed sleep that have nothing to do with weight.
Where did the story come from?
Dr Henri Tuomilehto and colleagues from the University of Kuopio and other academic and medical institutes in Finland carried out the research. The study was supported by the Kuopio University Hospital, the Juho Vainio Foundation, the Yrjo Jahnsson Foundation, the Jalmari and Rauha Ahokkaan Foundation and the Finnish Anti-Tuberculosis Foundation. It was published in the (peer-reviewed) medical journal American Journal of Respiratory and Critical Care Medicine.
What kind of scientific study was this?
Obstructive sleep apnoea is a condition where the upper airway collapses repeatedly during the night resulting in irregular breathing and disrupted sleep. Obesity is a known risk factor for this disorder and weight loss is known to improve symptoms (as well as reducing the risk of other weight-related disorders). The researchers say that although clinical guidelines recommend weight loss, there have been no randomised controlled studies that have assessed the effects of weight reduction on mild obstructive sleep apnoea.
This randomised controlled trial was set up to assess whether “intensive weight reduction and lifestyle intervention” improves outcomes in overweight patients with mild obstructive sleep apnoea. The researchers recruited 81 patients referred to Kuopio University Hospital with suspected sleep-disordered breathing between October 2004 and December 2006. All participants were between 18 and 65 years with body mass indexes (BMIs) ranging from 28 to 40kg/m2 and mild apnoea (5-15 events per hour) according to the apnoea-hypopnea index (AHI), an index used to assess the severity of this disorder. The patients were then randomly allocated to either an intervention group or a control group.
The intervention was a one-year lifestyle intervention that began with a 12-week very low calorie diet (600-800 kcal/day). Individual weight loss goals were decided and every second week the patient met with a nutritionist who gave advice on diet, exercise and positive lifestyle changes. Following the initial 12-week period, the participants were advised to maintain a low-fat diet and to increase their overall daily physical activity. In total, the participants in the intervention group were visited 14 times by the nutritionist over the year. Weight was measured at each visit and a questionnaire assessing quality of life was given at the beginning of the study and the three-month visit. Sleep recordings (where breathing during sleep was measured at home) were made at the beginning of the study, at three months and at one year, and scores were assigned on the AHI. The results of these cardiorespiratory readings were assessed by a trained doctor who didn’t know which group the participant was in (intervention or control). Height, weight, waist circumference and blood pressure were also measured at the beginning of the study, at three months and at one year.
The controls received a single counselling session (giving general dietary and exercise advice). After one year, the researchers compared the change in AHI and weight loss between the intervention and control groups.
What were the results of the study?
The researchers say that even though this was a randomised controlled trial, people in the intervention group were on average heavier, with a higher BMI and waist circumference. Before the study began, 89% of the intervention group were obese compared with 60% of the control group. Nine participants (five from intervention and four from control) dropped out. Weight loss was greater overall in the intervention group, compared with control (23.6 pounds versus 5.3 pounds (10.7kg versus 2.4kg)). After one year, changes in body weight, BMI and waist circumference were greater in the intervention group, although there were some changes in the control group.
At the three-month visit, symptoms of sleep apnoea were less severe in the intervention group than in the control group (AHI score: 5.3 events per hour with the intervention compared with 8.1 with control). This difference was maintained at one year. Overall, mild obstructive sleep apnoea was cured in 63% of the intervention group compared with 35% of the control group.
The intervention improved some aspects of quality of life and reduced snoring. Sleepiness seemed to reduce considerably in both groups after one year.
Using statistical models the researchers found that changes in severity of sleep apnoea were associated with changes in weight and waist circumference. A reduction in body weight of 11 pounds (5kg) meant a reduction of AHI by two (two fewer events per hour). The more weight that was lost also seemed to correspond to greater cure rates.
What interpretations did the researchers draw from these results?
The researchers say that intensive lifestyle counselling with an initial weight reduction programme can treat mild obstructive sleep apnoea and that benefits persist over a one-year period. This long-term maintenance of outcomes is crucial. They say that “a more aggressive treatment of obesity in patients with obstructive sleep apnoea is well founded”.
What does the NHS Knowledge Service make of this study?
This small, randomised controlled trial provides good evidence that weight loss is an appropriate treatment strategy for obstructive sleep apnoea. Clinical guidelines recommend encouraging weight loss in people whose obesity is contributing to their symptoms. This study supports this advice.
There are some issues to bear in mind when interpreting the results of this stuy:
- Despite being a randomised controlled trial, the intervention and control groups were not balanced when this study began. However, the researchers say they examined the interaction between BMI at the start of the study and the effectiveness of treatment and conclude that this did not have an effect. This means that the fact that the intervention group had greater BMI was unlikely to be a reason for the different treatment effects seen.
- It is important to point out that this study only looked at one particular cause of sleep problems, mild obstructive sleep apnoea. There are many other reasons for disturbed sleep that have nothing to do with weight.
- The study was small and the patients may have been a motivated group. The intervention was intensive, and the participants received a very low calorie diet, physiotherapist-supervised exercise sessions, and five initial visits over 10 weeks and 14 face-to-face follow-up meetings with a nutritionist over a year. As compliance can be a problem with lifestyle programmes, it is an important feature of this research that the researchers appear to have had success with these participants. Which parts of the programme actually contributed to the success, for example the regularity of follow-up visits with a nutritionist or the content of the advice offered, needs further evaluation.
A systematic review published by the Cochrane Library about lifestyle interventions (including weight loss, sleep hygiene and exercise) for obstructive sleep apnoea concluded that there was not enough evidence and that there is a need for randomised controlled trials of these commonly used treatments. This study provides stronger evidence that these are effective interventions, but leaves some further questions, such as: how intensive does the lifestyle intervention need to be to achieve success?