To sleep or not to sleep?
Daytime sleep reduces the risk of heart attack and stroke
Denis Gordeev, Naked Science
Daytime sleep is often studied in the context of labor efficiency: it has been shown that a short nap reduces drowsiness and improves the condition of workers. In earlier studies on the links between daytime sleep and cardiovascular diseases, it was found that short daytime sleep reduces mortality from these diseases.
However, subsequently, evidence was obtained that daytime napping, on the contrary, leads to an increased risk of heart and vascular diseases. A recent meta-analysis comparing 11 prospective studies explained that it could have been the duration of sleep. The graph of the dependence of the risk of illness on the duration of daytime sleep is "J-shaped". Lack of sleep gives a greater risk than a short (up to 30 minutes) sleep, which reduces the risk. But sleeping longer than half an hour again makes the risk grow.
But most studies compared only the presence or absence of daytime sleep, or only its duration, but not how often people sleep during the day. In addition, as a rule, only mortality from cardiovascular diseases was considered, and the effect of drowsiness on nonfatal cardiovascular diseases was studied much worse. Many studies do not take into account factors of sleep disorders and independent conditions.
In a new study published in the journal Heart (Häusler et al., Association of napping with incident cardiovascular events in a prospective cohort study), scientists consider the relationship between sleep regularity, its average duration and the risk of morbidity of both fatal and non-fatal cardiovascular diseases. The sample consists of 3,462 people, average age 57.1 years, who had no history of cardiovascular diseases.
During the follow-up (an average of 5.3 years), the participants developed 155 cases of cardiovascular diseases, both fatal and non-fatal. The risk was 48% lower in those who napped once or twice a week, compared with those who did not sleep at all. When taking into account additional factors (age, gender, education, smoking, sedentary lifestyle, body mass index, sleep duration at night and such primary risk factors for heart disease as hypertension, diabetes and dyslipidemia), the increase associated with daily daytime sleep and which was seen in the sample without taking into account additional factors was less significant.
In addition, no association was found between sleep duration and increased risk of cardiovascular disease. For people over 65, daytime sleep was less useful, but the influence of external factors may also affect here. Older people are more likely to accidentally doze off, which may be an indirect sign of ill health, and their day is less often subordinated to the work schedule, so they can sleep longer.
The results of the work can hardly be interpreted as an unambiguous "yes" to daytime sleep, but it can definitely be said that taking a nap periodically is more beneficial for the heart than complete abstinence from napping during the day.
Another point is related to the quality of night sleep. A rare nap during the day is associated with fewer heart diseases, only if a night's sleep is at least 6 hours a day. These studies are consistent with the results of an earlier study, which noted that a long day's sleep increased the risk of death from all causes – but only in those whose night's sleep was long enough. With a short night's sleep, a long day's sleep simply made up for the lack of sleep at normal times.
Scientists note that the mechanism of fixing the time, duration and causes of daytime sleep is imperfect, and this limits the application of the results of such studies. In the works devoted to sleep, it is important to strive to take into account such factors as its planning or spontaneity, regularity, whether it is a sign of ill health or lack of night sleep. In addition, restrictions are imposed by the lack of an adequate objective method for assessing drowsiness. Polysomnography, a generally accepted method for estimating the duration and stages of nighttime sleep, is impractical for measuring daytime sleep in population studies.
Actiography, used to assess sleep and wakefulness activity for 24 hours, is reliable for predicting total sleep time, sleep efficiency and sleep delay. But it is not capable enough to distinguish drowsiness from inactive wakefulness, especially in people who lead a sedentary lifestyle. There is an urgent need to develop an effective and feasible measure assessing drowsiness, which will allow a full assessment of health risks.
Portal "Eternal youth" http://vechnayamolodost.ru