Weight loss and quality of sleep: an interview with Kerry Stewart

Interview conducted by April Cashin-Garbutt, MA (Editor)Nov 26 2012

Please can you explain how you measure quality of sleep?

In our particular study we used a survey which consisted of 50 different questions which get at different aspects of sleep health. It was a patient self-report.

What problems can chronic sleep disruptions cause?

There are several different types of sleep disorders. We focussed mainly on the signs and symptoms of sleep apnea because that was likely to be most prevalent sleep disorder in our population, who were obese.

Sleep apnea is a condition in which patients have interrupted sleep because they are having difficulties keeping their airways open at night, so they are essentially gasping for breath. In layman’s terms they are almost choking. They have difficulty getting air into their lungs and this results in a drop in oxygen in their blood levels. This leads to a number of different problems.

What interrupts the sleep is that they wake up because their breathing stops or nearly stops and they wake up gasping for breath. This can happen multiple times during the night. That leads to disrupted sleep patterns, which would also be evident during the day because they haven’t gotten a good night’s sleep. This leads to daytime fatigue and sleepiness to the point where some people are at risk of falling asleep during the day, which can be dangerous if they are driving a car for example.

Also, sleep disordered breathing is associated with a high risk for cardiovascular disease. People who have sleep apnea, in particular, have a much higher risk of heart attacks, stroke, peripheral arterial disease, hypertension and so forth. There is also the primary metabolic disorder associated with a lack of sleep, this is because sleep apnea can affect metabolism, so they can end up getting an increasing their body weight and have an increased risk of diabetes.

One of the real questions is what comes first: sleep apnea or obesity? One of the risk factors of obesity is sleep apnea is weight gain, but having sleep apnea can lead to further weight gain, so you create this vicious cycle. Then all the other problems I mentioned tend to get worse.

To some extent it is like the chicken and the egg. We are not really sure where to break the cycle to be most effective. The primary medical treatment for sleep apnea is continuous positive airway pressure (CPAP) where people wear a mask at night which forces air down to the lungs to keep the airways open so they can get enough oxygen. This can reduce the severity of sleep apnea, but it is not very pleasant and a lot of people don’t like using it. Also, it doesn’t necessarily deal with the underlying cause of sleep apnea, which is thought to be obesity.

What I have so far been discussing is obstructive sleep apnea, there is another form of sleep apnea of the central nervous system, but the primary form of apnea is obstructive sleep apnea.

How did your research into weight loss and quality of sleep originate?

We’ve been working with patients for many years doing exercise and diet interventions for people with obesity and hypertension and it became clear that several people would tell us that they have problems sleeping. Then in talking to our colleagues in the pulmonary division who practice sleep medicine it became clear that the patients we were dealing with, the ones we were trying to get to lose weight and reduce their blood pressure, are actually the people that are most likely to have sleep apnea.

We collaborated and realised that in addition to the medical treatments that are available to improve sleep quality, lifestyle changes can also have a major impact. Some of our colleagues have done some weight loss interventions over the years on people with sleep apnea and it has been shown that it does contribute to a reduction in sleep apnea symptoms and the severity of it.

In this particular study we didn’t select people because they had sleep apnea, they all just carried out the sleep disturbance survey, and the finding emerged that when there was weight loss, it was associated with an improvement in self-reported symptoms that would suggest that they a better quality of sleep, particularly if the weight loss was in the belly.

The standard way of assessing whether someone has sleep apnea is by doing a sleep study. You either have a patient at home, or more likely in a laboratory and you do overnight measurements where you measure their breathing patterns, blood oxygen levels, their sleep patterns etc. You can more definitely document that they have a medical condition. The survey that we did is quite good in the sense that if people have scores that suggest sleep apnea, they are likely to have it to some degree.

Please can you outline the study that took place?

The unique feature of our study is that we were interested in looking at the comparison of diet versus diet plus exercise. Our hypothesis was that you would get more benefit from a diet and exercise combination on a variety of measures, in addition to the sleep measures including several cardiovascular parameters we were interested in.

What did your research find?

We found that weight loss, particularly if the weight was primarily lost in the trunk or the belly fat, was associated with improved sleep quality as reported on this survey. It didn’t matter if you did diet or diet plus exercise, the sleep improvement was related to how much weight you lost.

Why do you think it didn’t matter if the patients were just dieting or were dieting and exercising?

Some studies actually have suggested that exercise alone would decrease the severity of sleep apnea. Although we were not really sure if these patients did have sleep apnea, we were more focussed on the self-reported symptoms of having sleep disturbances.

Also, the study may not have been large enough to separate out the separate effects of diet and exercise. I think if we did a larger study, which is our plan, where we could tease out whether or not exercise and weight loss had independent effects or if they have synergistic effects. Our hypothesis would be that the best approach of dealing with obesity related problems, of which sleep disturbance is one, would be by a more comprehensive and intense lifestyle change, which would result in people having more weight loss, more belly fat loss and higher levels of fitness.

Did your research show whether the association between overall weight loss and sleep quality was causative? Is this plausible?

It’s suggestive because when we did the analyses, the amount of weight loss was correlated with the degree of improvement in sleep quality. That is a very plausible biological relationship. Other studies have detected somewhat similar patterns, so we think it is real.

Why do you think that improvement in sleep quality was especially associated with loss of belly fat?

One of the reasons why obesity is associated with sleep apnea in particular is that the fat accumulating in the belly takes up space and it reduces the ability of the lungs to expand. Also fat tends to accumulate in the neck, which surrounds the trachea, so the amount of effort it takes to get air into the lungs is increased – it gets harder to breathe because there is a mechanical resistance.

We also know that fat can disturb a lot of other processes that go on in the body, for example, it is a source of inflammation, and that can affect the way the body responds in a variety of ways, in particular, it could affect breathing patterns.

But we think it is likely to be due to mechanical pressure – resistance because the fat is taking up space in the lungs and so the lungs and the trachea can’t expand in the way it needs to in order to breath normally.

What impact do you think this research will have?

We hope that it raises awareness of the fact that, besides all of the other things that we know obesity is associated with - that is heart disease, diabetes and multiple other health problems - it is also associated with sleep disorders. To the extent that people lose weight they will not only improve all the other conditions that they might have, it should also improve sleep quality. If you could break this vicious cycle and improve sleep health, you can get a lot of bang for the buck from weight loss because it affects so many other conditions.

We hope that our work will raise awareness and for people who have problems sleeping and overweight, this is yet another reason to lose weight.

Do you have any plans for further research into this topic?

We have a couple of grants that are being evaluated as we speak that would look at the relationships between sleep apnea, cardiovascular health and the extent to which diet and exercise can improve not only sleep disorders but reduce the risk of cardiovascular disease, which is one of the major consequences of having sleep apnea.

Would you like to make any further comments?

We are doing a similar study of diet and exercise in older people who are at risk of frailty. We think that having sleep apnea actually makes the frailty worse. We are hoping that by putting people on a weight loss and exercise programme, it will not only improve muscle strength and cardiorespiratory endurance but it will also help them sleep better and reduce the severity of sleep apnea. Also we hope it will improve their overall physical state so that they are less frail and, will hopefully reduce their risk of falling, which is a major problem in older people.

So far the data is really encouraging, with improvements in all of the parameters that we measure, to some extent even more so than in younger people. This may be because their problems may be worse to begin with, so their magnitude of improvement seems to be better.

Another important point is that this problem of sleep disturbances can occur at any age but the prevalence is very high in people who are overweight or obese. It has been estimated that the prevalence of people who have obesity that have sleep disorders is in the range of 40-60% and if you have diabetes on top then this risk increases even further. So if someone is obese and has diabetes then the likelihood that they have a real sleep problem is probably in the range of 70-80%.

Poor sleep health is also something that often goes undiagnosed or ignored - people often put up with their spouse complaining at their snoring or maybe they don’t have it severe enough that they are choking. The problem with tolerating it is that if you do have sleep disturbances, which can degrade your health and will aggravate all the risk factors that you may have for heart disease. So the probability of having a cardiac event keeps increasing.

Somewhere in this cycle it really needs to be broken. We are most interested in studying the extent to which lifestyle change can help. This is because it really gets at the underlying problem that leads to sleep disorders like sleep apnea in the first place. Again you can treat sleep apnea medically, but if you stop treating it medically it comes right back and you are not getting at the underlying cause. We are more interested in how you can really make the problem go away to the extent possible.

About Kerry Stewart

Dr. Kerry J. Stewart is Professor of Medicine at the Johns Hopkins School of Medicine and director of clinical and research exercise physiology. In this role, he directs exercise testing and training programs and is the program director for cardiac rehabilitation at Johns Hopkins.

He is a Master of the American Association of Cardiovascular and Pulmonary Rehabilitation, Fellow of the American Heart Association and Fellow of American College of Sports Medicine. He was the AACVPR Award of Excellence recipient in 2009.

Dr. Stewart's clinical and research interests are in the area of exercise testing and training and body composition of patients with chronic health conditions including diabetes, coronary artery disease, obesity, hypertension, obstructive sleep apnea, and peripheral artery disease, coronary risk factor assessment and modification in older adults, and patients with implanted devices.

He has been the principal investigator of several NIH funded grants that have addressed the growing public health problem of diabetes and obesity by examining the effects of weight loss and exercise interventions on parameters of cardiovascular structure and function that are markers of preclinical cardiovascular disease.

Within these studies, he has also studies effects on quality of life, and in particular, sleep health. He has participated in clinical and community based trials focused on improving chronic health conditions through lifestyle interventions and education.