While there is likely to be a metabolic relationship between sleep and cholesterol measurements such as triglycerides, this link has not been clearly established. Thus, the relationship between sleep and cholesterol is best explained at the moment by lifestyle. For example, in the Japanese study, there was a high correlation between the women and men who slept 6 hours or fewer per night and several unhealthy habits that can increase cholesterol. Many of those men and women who slept fewer than 6 hours also reported in the study that they skipped meals, ate out once or more per day, and/or experienced high levels of psychological stress.
Sleep fragmentation was induced by a treadmill which moved intermittently for 3 s with 30-second pauses between moves. Blood lipid and lipoprotein profiles and adiponectin, leptin, ghrelin, cortisol, epinephrine, and norepinephrine levels were compared among four groups including rats with ad libitum sleep and ad libitum intake (Control), those exposed to sleep fragmentation with ad libitum intake (SF), those with ad libitum sleep and diet restriction (DR), and those exposed to sleep fragmentation and diet restriction (SF+DR). SF and SF+DR showed a higher ratio of LDL and HDL cholesterol (184% and 132% increase, P-value for SF effects <0.001) and ghrelin (64% and 18% increase, P-value for SF effects <0.01) and lower leptin (76% and 44% decrease, P-value for SF effects <0.001) and adiponectin levels (3% and 18% decrease, P-value for SF effects <0.01) than Control.
The effect sleep has on lipids highly varies and appears to affect genders differently. In some studies, no significant difference between sleep and lipid profiles were noted, while other studies revealed that too little or too much sleep affected HDL, LDL and/or triglycerides.
For women, HDL and triglyceride levels appeared to be more affected by sleep duration than men in some studies. In some of these cases, HDL was lowered by up to 6 mg/dL and triglyceride levels were increased by up to 30 mg/dL in women who slept less than six hours or more than eight hours. In most of the studies conducted to date, LDL did not appear to be significantly affected by sleep patterns.
Sleep patterns appeared to have a different effect on men. Some studies suggested that LDL increased by up to 9 mg/dL in men who slept less than six hours. In most of these studies, triglycerides and HDL cholesterol did not appear to be significantly affected.
One study also revealed that getting too much sleep (greater than eight hours) or too little sleep placed individuals at higher risk of metabolic syndrome, which is a constellation of signs and symptoms that include lowered HDL, raised triglyceride levels, obesity and elevated blood pressure and glucose levels.
