I wrote a research paper looking the relationship between sleep duration and metabolic syndrome and this blog is a summary of what I learned. References are listed at the end and can be found on PubMed.
Metabolic Syndrome and sleep
Metabolic syndrome is a group of metabolic risk factors used to identify individuals at risk for cardiovascular disease (1). A correlation between sleep duration and the development of metabolic syndrome has been observed.
The National Cholesterol Education Program (NCEP) Adult Treatment Panel III diagnosis of metabolic syndrome requires the presence of three or more of the following features (1):
1. Waist circumference:
- Men: Greater than or equal to 102cm (40in)
- Women: Greater than or equal to 88cm (35in)
2. Triglycerides: Greater than or equal to 1.7mmol/L (150 mg/dL)
3. HDL cholesterol:
- Men: Less than 1.0mmol/L (40mg/dL)
- Women: Less than 1.3mmol/L (50mg/dL)
4. Blood pressure: Greater than or equal to 130/85 mmHg or medicated for hypertension
5. Fasting blood glucose: Greater than or equal to 5.6mmol/L (100mg/dL) or medicated for hyperglycemia
First-line treatment focuses on lifestyle factors such as dietary modification and increased physical activity (1). However, given that “‘normal’ average sleep duration has decreased from about 9 h per night in 1910 to about 7.5 h currently, (2)” and mounting evidence that sleep deprivation causes physiological changes that lead to metabolic syndrome, sleep deprivation is another important lifestyle factor to consider.
Short sleep duration (less than 6 hours per night) is associated with the highest risk for metabolic syndrome, but long sleep duration (more than 8 or 9 hours per night) is also associated with increased risk. The lowest risk was seen in subjects sleeping 7-8 hours per night (3,4).
Belly fat and sleep
With regards to abdominal obesity, “very short and short sleepers were at least 1.6 times more likely to meet criteria for abdominal obesity … compared with individuals who slept 7 to 8 hours per night (4).”
There is also a correlation between insulin resistance and sleep duration, both short and long: “with the reference group, the odds of meeting the glucose criterion were at least 1.7 times greater in the very short (< 6 hours) and long (> 8 hours) sleeper groups (4).” It is also likely that insulin resistance due to altered metabolism resulting from inadequate sleep develops gradually over years. One study restricted sleep in healthy young men to four hours per night for six nights and found that sleep debt led to impaired carbohydrate tolerance. Decreased morning insulin sensitivity was observed after 6 days of sleep restriction compared to when subjects were fully rested (6). “These results suggest that insulin sensitivity was lower on the 6th than on the 5th day of sleep restriction and thus that insulin resistance may develop progressively with increasing exposure to partial sleep loss (5).”
Blood pressure and sleep
The Sleep Heart Health Study found that sleep duration was associated with risk of hypertension, with those sleeping less than 6 and 6-7 hours and those sleeping 8-9 and 9 or more hours demonstrating increased risk (6). A longitudinal analyses of the first National Health and Nutrition Examination Survey demonstrated that sleep durations of “< or =5 hours per night were associated with a significantly increased risk of hypertension … in subjects between the ages of 32 and 59 years (7).”
Can you sleep too much?
The studies discussed above have also found a relationship between increased sleep and metabolic syndrome. When examined more closely in one study, relationships between long sleep duration and metabolic syndrome and elevated glucose “were no longer significant with adjustment for use of antihypertensive medication, which has been shown to impact fasting blood glucose levels (4).” There is also a relationship between long sleep duration and sleep apnea, suggesting that “long sleep duration is a proxy for sleep disordered breathing and that sleep apnea drives the relationship between long sleep duration and health outcomes (4).”
What about sleep quality?
Sleep quality is also an important factor to consider. An observational, cross-sectional study demonstrated that “poor global sleep-quality scores on the Pittsburgh Sleep Quality Index were related significantly to the presence of the metabolic syndrome (8).”
Criticism and conclusions
Studies relating sleep duration to metabolic changes are often confounded by pre-existing conditions (such as diabetes or hypertension), lifestyle habits (such as smoking, diet, alcohol intake, and caffeine intake), and other factors affecting sleep (such as sleep apnea). It is therefore important that studies of sleep duration take these factors into account and control for them as much as possible in order to establish a clear relationship between sleep and health outcomes. One researcher has challenged the above conclusions by offering three criticisms. First, “few obese adults/children are short sleepers, and few short sleeping adults/children are obese or suffer obesity-related disorders (9).” Second, the clinical risk only emerges from very short or long sleep duration and develops over many years, so while acute sleep restriction does lead to leads to glucose intolerance and metabolic syndrome “this is too little sleep and cannot be sustained beyond a few days (9).” Finally, he offers an alternative explanation for the relationship between sleep and metabolism: “habitually insufficient sleep could contribute towards obesity, metabolic syndrome, etc., via sleepiness-related inactivity and excess energy intake (9).”
It seems obvious that sleep is an important factor in health, but it is often overlooked by both conventional and naturopathic practitioners. Based on the studies discussed, the optimal sleep duration is between 7-8 hours per night. Many patients fail to prioritize sleep or have trouble falling asleep easily, both issues that can be greatly aided by naturopathic interventions. Sleep quality is also an important consideration and naturopathic doctors are also well equipped to make recommendations in this area.
- MD Consult. Metabolic Syndrome. Accessed 18 Nov 2008. Available at: http://www.mdconsult.com.
- Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999 Oct 23;354(9188):1435-9.
- Choi KM, Lee JS, Park HS, Baik SH, Choi DS, Kim SM. Relationship between sleep duration and the metabolic syndrome: Korean National Health and Nutrition Survey 2001. Int J Obes (Lond). 2008 Jul;32(7):1091-7. Epub 2008 May 13.
- Hall MH, Muldoon MF, Jennings JR, Buysse DJ, Flory JD, Manuck SB. Self-reported sleep duration is associated with the metabolic syndrome in midlife adults. Sleep. 2008 May 1;31(5):635-43.
- Knutson KL, Spiegel K, Penev P, Van Cauter E. The metabolic consequences of sleep deprivation. Sleep Med Rev. 2007 Jun;11(3):163-78. Epub 2007 Apr 17. Review.
- Gottlieb DJ, Redline S, Nieto FJ, Baldwin CM, Newman AB, Resnick HE, Punjabi NM. Association of usual sleep duration with hypertension: the Sleep Heart Health Study. Sleep. 2006 Aug 1;29(8):1009-14.
- Gangwisch JE, Heymsfield SB, Boden-Albala B, Buijs RM, Kreier F, Pickering TG, Rundle AG, Zammit GK, Malaspina D. Short sleep duration as a risk factor for hypertension: analyses of the first National Health and Nutrition Examination Survey. Hypertension. 2006 May;47(5):833-9. Epub 2006 Apr 3.
- Jennings JR, Muldoon MF, Hall M, Buysse DJ, Manuck SB. Self-reported sleep quality is associated with the metabolic syndrome. Sleep. 2007 Feb 1;30(2):219-23.
- Horne JA. Short sleep is a questionable risk factor for obesity and related disorders: statistical versus clinical signiﬁcance. Biol Psychol 2008;77:266-76.