Sleep has previously been related to chronic health conditions, such as depression, obesity, and hypertension. But does this relationship hold all over the world? Given that every culture and country has differing lifestyles (diets, activity levels, healthcare systems, etc.), could it be that sleep quality is not predictive of chronic disorders outside of the US?
A few large datasets that included self-reported sleep and health data from Finland, Poland, Spain, China, Ghana, India, Mexico, Russia, and South Africa were analyzed and compared. The prevalence of chronic conditions, including angina (chest pain), arthritis, asthma, chronic lung disease, depression, diabetes, hypertension, obesity, and stroke were all analyzed and related to sleep duration.
So, first of all, how did everyone sleep? The prevalence of self-reported sleep issues ranged from 2.8% to 17% of the population. China reported the lowest amount of sleep problems with 2.8%, while 15% of the Indian population and 17% of the Polish population reported sleeping issues. What’s more, there was a large difference in the prevalence of chronic conditions between countries. The authors of this study report, for example, that angina was reported in 2.8% of the Mexican population, but in a whopping 31% of the Russians. Additionally, only 0.3% of the Chinese population reported depression, while that number rose to 22.6% in the Spanish population. Differences in self-reported diagnosis may stem from the fact that cultures have different health habits and also express themselves (as in the case of depression) very differently.
Not surprisingly, many of the chronic conditions were related to sleep problems. In fact, all of the chronic diseases except for chronic lung disease, hypertension, and obesity were related to sleep problems. There were individual differences between countries, though. For example, angina was predictive of sleep problems in all countries except for Mexico (who has a very low level of angina to begin with). Diabetes was linked with sleep problems in every country besides India. Depression was linked with sleep problems in every country, but, surprisingly, self-related hypertension and obesity were not related to sleep in any of the countries. Overall, a combined measure showed that for each chronic condition that the participants reported, their sleep became worse and worse.
Importantly, although interesting, this study is limited by the fact that all measures of chronic conditions and sleep problems are self-reported. Certain conditions (hypertension, for example) may be under-reported in this population. An under-reporting of conditions can skew results. Also, because “sleep problems” has been lumped into one, those with chronic sleep issues could be combined with those who have occasional sleep problems. Additionally, as you may have noticed, sleep apnea was not discussed! It is unknown how apnea plays a role in these results, and we can only assume that sleep apnea was indeed one of the “sleep problems” that some of the subjects referred to. It can be assumed that having poor quality sleep of any kind influences health, and it is important to realize that this study does indeed generalize to those who have untreated sleep apnea. And although this study discusses chronic ailments as if they cause sleep issues, I would be willing to bet that a lot of sleep problems cause the chronic illnesses. Just in case my (absolutely correct) prediction is indeed true, stick to your sleep apnea treatment!