2. Sleep, disease and vulnerable groups


Many studies have observed an association between mortality risk and lack of sleep (sometimes considered to be fewer than 7 hours and others, fewer than 6) or excess sleep (generally more than 9 hours a day). As Sudan Redline, professor of medicine at Harvard Medical School, explained at the B·Debate session, a significant part of this risk is due to the increase in cardiovascular diseases. Sleep, especially in the non-REM phase, seems to have a cardioprotective function. Any alteration, in quantity or quality, has a negative effect on the mechanisms that regulate hunger and insulin metabolism, increasing the risk of obesity. This is why both too much and too little sleep seem to be firmly tied to the risk of diabetes, high blood pressure, stroke and coronary disease.

The connection with cancer is still up for debate, but the evidence is starting to pile up. Ramón Farré, professor of Physiology at the University of Barcelona,​​ explained “The data is still scarce and recent, and studies in both human and animals have their limitations. Nevertheless, they meet several of the classical criteria of causality.”

These studies include observations of animals in which fragmented sleep increases the risk of developing tumors. And, above all, studies in humans that have found a relationship between sleep apnea (a disorder that causes the patient to stop breathing while sleeping, affecting the quality and depth of sleep) and a huge increase in the frequency of certain types of cancer in patients over 60.

In addition to the increase in diseases associated with sleep quality, some ages and groups are particularly vulnerable to its effects. Problems like insomnia and apnea, among others, are relatively frequent in pregnant women, for example. María Luz Alonso-Álvarez, head of the Sleep Unit at Hospital Universitario de Burgos, lamented the fact that there are still very few studies that analyze the consequences of this, even though some have pointed to increased risk of gestational diabetes and postpartum depression, as well as more complicated birth and the need for cesareans. Thus, she believes it is necessary to establish what is healthy sleep for each trimester of pregnancy. It is also worth stressing how important it is for children to get enough quality sleep, depending on their age: It is a key element in their cognitive development and can even predict their risk of being obese in the future, as noted Oscar Sans, medical director at AdSalutem Institute and head of the Sleep Unit at Hospital Sant Joan de Déu in Barcelona.

Adolescence is a particularly problematic age for sleep. The National Sleep Foundation recommends teens sleep more than adults, between 8 and 10 hours a day. But 45% of them don’t even get 8 hours. Plus, there is a ‘phase delay’ that occurs at this age, shifting circadian rhythms later into the night, so it is harder to fall asleep.

According to Leila Kheirandish-Gozal, professor of Pediatrics and director of the Child Health Research Institute at the University of Missouri School of Medicine, this affects memory and attention span, leading to poorer performance at school. But also to metabolic issues, greater risk of depression and anxiety, and of taking drugs and drinking. This is why, in addition to educating and promoting healthy sleep habits, some are studying the option of starting the day later at high schools. One study estimated the possible benefits at $8.6 million over two years in the United States alone (mainly due to the increased performance and decreased chance of accidents), although there are also cons that would have to be studied and addressed.

Too much screen time is another problem. US teens spend an estimated 6 to 7 hours in front of a screen. Kheirandish-Gozal recommends disconnecting from all screens at least one hour before going to bed, as the light can make it harder to fall asleep. But there is no solid evidence yet. Jamie Zeitzer, associate professor at Stanford University, pointed out that we don’t yet know if this amount of light is relevant, and alluded to the role screens play in social interaction, which would be an inadvisable stimulant before bed.

Another group that is especially sensitive are the elderly. We tend to assume that, physiologically, they need less sleep. But, according to Sonia Ancoli-Israel, professor emeritus at the University of California, San Diego, “It isn’t clear that the need for sleep decreases, but the ability to do so does”. Although there is some change in circadian rhythms, “Age doesn’t have the biggest impact on this; it is everything else that goes along with it.” Sleep issues in the elderly tend to have more to do with the diseases that normally come with age and make it hard for them to rest, as well as the various medications they are generally taking that can have an impact. This is not only highly relevant to their quality of life but can also make diagnosis more difficult. “Lack of sleep leads to memory and attention problems,” explained Ancoli-Israel, “which can lead doctors to, mistakenly, suspect dementia.”