Virtually all animals, certainly all mammals, sleep. While the form and shape of sleep can vary, sleeping is a universal phenomenon. Even fish sleep, though their eyes remain open.
Sleep disorders like sleep apnea ("apnea" = without breathing) are growing in prevalence nationwide as the country gets fatter and fatter. Our throats assume a smaller diameter, even our tongues get obese. This results in intermittent obstruction to the airway during sleep, causing snoring. It also results in sleep interruption, particularly during attempts to "descend" down to the deepest phases of sleep. Dire health and cardiac consequences can sometimes emerge, such as high blood pressure, higher blood sugar, abnormal heart rhythms, impaired heart muscle function, even sudden death.
We are all familiar with the perceptible effects of sleep deprivation: edginess, crabbiness, diminished attention span, slowed reaction time. I'm not talking about sleep apnea or sleep disorders, but just simple duration of sleep. Data are emerging that both sleep deprivation and sleep excess may trigger undesirable changes in lipids (cholesterol values):
Associations of usual sleep duration with serum lipid and lipoprotein levels.
Kaneita Y, Uchiyama M et al.
STUDY OBJECTIVES: We examined the individual association between sleep duration and a high serum triglyceride, low HDL cholesterol, or high LDL cholesterol level. DESIGN AND SETTING: The present study analyzed data from the National Health and Nutrition Survey that was conducted in November 2003 by the Japanese Ministry of Health, Labour and Welfare. This survey was conducted on residents in the districts selected randomly from all over Japan. PARTICIPANTS: The subjects included in the statistical analysis were 1,666 men and 2,329 women aged 20 years or older. INTERVENTION: N/A. MEASUREMENTS AND RESULTS: Among women, both short and long sleep durations are associated with a high serum triglyceride level or a low HDL cholesterol level. Compared with women sleeping 6 to 7 h, the relative risk of a high triglyceride level among women sleeping
<5 h was 1.51 (95% CI, 0.96-2.35), and among women sleeping > or =8 h was 1.45 (95% CI, 1.00-2.11); the relative risk of a low HDL cholesterol level among women sleeping
<5 h was 5.85 (95% CI, 2.29-14.94), and among women sleeping > or =8 h was 4.27 (95% CI, 1.88-9.72). On the other hand, it was observed that the risk of a high LDL cholesterol level was lower among men sleeping > or =8 h. These analyses were adjusted for the following items: age, blood pressure, body mass index, plasma glucose level, smoking habit, alcohol consumption, dietary habits, psychological stress, and taking cholesterol-lowering medications. CONCLUSIONS: Usual sleep duration is closely associated with serum lipid and lipoprotein levels.
Triglycerides go up with too little or too much sleep. Note especially the extraordinary association of low HDL cholesterol with sleeping
<5 hours (nearly 6-fold increased risk) or sleeping >8 hours (more than 4-fold increased risk).
Why do these effects develop? Does sleep deprivation, for instance, trigger higher adrenaline levels, encourage carbohydrate cravings or binges, make us less likely to engage in physical activity? Cortisol is elevated; could this be a factor? I know that I am a different person when sleep-deprived: irritable, less clear-thinking, quicker to anger, more critical, and I develop carbohydrate cravings. It's curious that triglycerides increase when sleep excess is present; what might that represent?
Anyway, the data are growing: Sleep is an important facet of health, both for maintaining a bright outlook and to discourage development of low HDL and high triglycerides. Though not specifically examined in this study, we know that low HDL/high triglycerides are, as a rule, associated with the undesirable small LDL particle pattern.
As a practical matter, you may also find sleep and waking from sleep more satisfying and restful if you sleep in increments of 90 minutes, e.g., 7 1/2 hours (rather than 7 or 8 hours). This is because the full cycle of sleep, from phase 1 to REM (rapid-eye movement sleep), requires 90 minutes for completion. That doped feeling that sometimes develops when awaking will disappear if you sleep according to your sleep cycle, which is usually 90 minutes long.