Sleep Patterns Across the Lifespan

Want to know my New Year's resolution? "Go to bed earlier and get more sleep". For our March 2016 issue  Elena Kochova researched why some people need more sleep than others. 

We are all familiar with the concept of ‘sleeping like a baby’. But why do babies sleep so much (other than to keep parents sane)? What is the difference between the quality of sleep in a newborn and, say, an 80-year old?

The Dreaming Fetus

National Sleep Foundation

Sleep patterns can be seen even in the fetus, whose main job is, in fact, to sleep in the cozy womb while being devotedly nourished by his sleep-deprived mother. The wake-sleep cycle emerges somewhere around 32 weeks of gestation; both ‘active’ and ‘silent’ sleep phases can be distinguished, comparable to REM (rapid eye movement) and NREM (non-rapid eye movement). Short periods resembling the waking state interfere, but are still immature and disorganized; they comprise only 5% of fetal life. The spontaneous twitching (“kicking”) of the fetus is more indicative of REM sleep than wakefulness [1] and is essential for the development of somatosensory maps in the brain [2]. Precisely how sleep "happens" is far from understood, but these findings show that sleep generator neurons mature prior to other brain areas and that sleep plays a role in the overall development of the neocortex.

Sleeping Like a Baby

Right after birth, newborns encounter a new problem: food. With a small stomach they have to eat frequently and save energy for their incredibly fast growth. In the first days the average newborn sleeps around 18 hours a day, which comes down to 14 hours by the end of the first month. Similarly to the fetus, ‘active sleep’ is interchanged with ‘quiet sleep’ – the deep sleep that enables babies to sleep through a concert. Each comprises approximately half of sleeping time. As the baby grows, feeding become less frequent and the circadian sleep rhythm starts to develop; usually at about 7 months, infants sleep mostly at night, with a few naps during the day. The latter tend to condense with time and the sleeping pattern becomes stable. Toddlers will usually sleep 10-12 hours every night while afternoon napping gradually becomes less important and disappears by the age of 5 years.

Puberty and Adolescence

Somewhere after the age of 10, a significant change in the sleep pattern occurs. It is no coincidence that this is when her majesty – puberty, the queen of all disturbances – kicks in. We often blame social interactions for teenagers’ nocturnal behavior, but the drive to fall asleep late in this population, in fact, has a physiological background. The pubertal changes alter the homeostatic and circadian regulation of sleep resulting in a shift in the circadian rhythm of 1-3 hours. 

SLEEP PATTERNS 

REFLECT GENERAL HEALTH

The tendency to fall asleep later is different between girls and boys, as is the onset of puberty, and it is also more pronounced in boys. They tend to be more active in the evening and sleepy during the day. Teenagers have an internal clock that interprets environmental time cues differently from adults. The need to wake up early for school and the need for more sleep causes sleep deprivation in most teenagers. Grades go up when teenagers go to school later in the day [3].

Animal studies show similar changes in sleep patterns around the time of sexual maturation in mice, rats and monkeys [4]. In addition, removal of the gonads and the administration of estrogen, testosterone, or progesterone produce immediate effects on the circadian properties and sleep architecture of adult rodents [5].

Adulthood

In the early twenties, the sleep delay and sleep need are balanced at about 8 hours. It is thought that the need for sleep diminishes in older adults; in fact, what changes is the sleep architecture – it is more difficult falling and staying asleep. Sleep becomes a less restorative and less satisfying reward. There is yet another shift in the circadian rhythm: the elderly go to bed and wake up earlier compared to younger adults – a sleep phase reminiscent to that of early childhood. The sleep is fragmented with frequent awakenings, often causing daytime sleepiness and the tendency to ‘doze off’. The reason for these changes in sleep rhythms with age is not clearly understood. The prevalence of insomnia and sleep apnea increases with age, especially in men. Pregnancy and menopause cause drastic changes in women as well, further indicating that hormones play a role in the circadian rhythm and homeostatic drive. Associated medical problems and medications certainly contribute to sleep disturbances. 

THE MORE TIME PEOPLE HAVE,

THE LESS THEY ARE ABLE TO SLEEP

It appears that the more time people have, the less they are able to indulge in sleep. But sleep patterns are both a reflection of, and an influence on, the overall health of a person. Certain acute and chronic factors (caffeine or alcohol intake, exercise and nutrition, stress level) are major factors in sleep hygiene. Until science provides more detailed answers about the precise role of sleep, we continue with the vague knowledge that we need sleep for our physical and mental wellbeing.

With that I leave you, hoping that reading this has not augmented your sleep need.

[1] Karlsson et al.,. Plos Biol,  2005

[2] Khazipov et al., Nature, 2004

[3] Wolfson et al., Sleep, 2003

[4] Hagenauer et al., Dev Neurosci, 2009
[5] Karatsoreos et al., Endocrinology, 2007 

by Elena Kochova, Master's student MedNeuro
this article originally appeared March 2016 in Volume 09 Issue 1 "The Aging Brain"