Studies show time and again that people who sleep poorly are more often overweight. A Spanish study has now examined what is behind it in twins.
An army of the sleepless walks the world, driven by alarm clocks, deadlines, telephone conferences, and glare of light wherever you look. The average length of sleep has been reduced by at least 1.5 hours in the last 100 years. The greatest enemy of sleep is tension. One of its consequences could be obesity, as has now been shown again.
Studies have shown for years that people who sleep poorly or not enough often have to bear more weight. Researchers around Jean-Philippe Chaput from Laval University in Quebec, for example, reported in 2008 in the journal Sleep that short sleepers had a 27 percent higher risk of gaining five kilos than normal sleepers in the six years of the study (1). There are many similar studies. It has to be said, however, that this is only a statistical connection. Whether excess weight is a direct result of sleep deprivation cannot be shown with such an examination. And there may be other factors that contribute to sleep deficiencies, as well as excessive food or lower calorie consumption. In order to get a little more light into this thicket, the Spanish researchers around Juan R. Ordonana have now worked with identical and non-identical twins (2).
The scientists examined 2150 twins born between 1939 and 1966. They not only wanted to know how well they were sleeping or what their scales indicated, but they also asked them how much they were moving, whether they were smoking, or feeling anxious or depressed. All these factors could have an impact on the results of the study. As expected, the researchers initially saw a strong correlation between the twins’ sleep and their body mass index (BMI), the measure of weight in relation to body height.
Afterward, however, they looked at siblings who differed either in their BMI or their sleep quality. The connection between sleep and BMI was only strong if the researchers selected sibling pairs that differed in their weight. This did not change when they removed childhood genetic factors or early environmental influences. If, on the other hand, the scientists looked at twin siblings who slept differently, the picture changed. Now the BMI did not seem to affect the quality of sleep any further. The results, therefore, support the assumption that sleep quality influences BMI and not vice versa. The worse the sleep, the greater the probability of an increased BMI, is what the scientists stated in their publication in the Journal of Sleep Research. Genetic causes do not seem to play a role here, as they did not differ significantly between identical and dizygotic twins.
Although this study is no proof of a causal connection, it again confirms the suspicion that it is the lack of sleep itself that causes the weight to increase. Scientists have different theories about what happens in the body. On the one hand, a drowsy body turns down the body temperature and is less active. This also reduces the basal metabolic rate, i.e. the number of calories that it normally burns at rest. In addition, the overtired brain sends out hunger signals. A little sleep lowers the leptin levels and increases the blood concentration of ghrelin, thus increasing appetite. Some researchers also suspect that a change in intestinal bacteria (microbiota) could increase the weight of bad sleepers. They now have to investigate this in further studies.
This is part 17 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website. Translation was done with the assistance of DeepL translator.
- Chaput JP, Després JP, Bouchard C, Tremblay A. The association between sleep duration and weight gain in adults: a 6-year prospective study from the Quebec Family Study. Sleep. 2008 Apr;31(4):517-23
- Madrid-Valero JJ, Martínez-Selva JM, Ordoñana JR. Sleep quality and body mass index: a co-twin study. J Sleep Res. 2017 Aug;26(4):461-467