Sleep is one area where our knowledge has considerably advanced with improved research technologies and the current view by many medical experts is that sleep is one of the vital determinants of health alongside nutrition, exercise and public health.
Unfortunately, over the last 10 years we have seen increasing evidence that chronic partial sleep loss is implicated in dementia, heart disease, cancer, obesity and type 2 diabetes. This obviously gives cause for concern when we know that poor quality sleep is becoming increasingly common - indeed in the US it was reported that more than 30% of adult men and women between the ages of 30 and 64 years sleep less than 6 hours per night.
So what is the right amount of sleep?
The University of Western Ontario, carried out the World’s biggest sleep study with 44,000 people taking part in 2018. There is a video about this study here
This presented several conclusions:
- Most participants who slept 4 hours or less performed as if they were 9 years older
- Regardless of age or gender, 7 or 8 hours of sleep resulted in the best cognitive function
- Reasoning and verbal skills are impaired by both too little and too much sleep.
So, it is significant to observe that the trend for the shorter sleep duration of 6 hours has developed over the same time period as the dramatic increase in the prevalence of obesity and type 2 diabetes.
In the US the increase in overweight children went from about 5% in 1971 to about 15% in 2004. An increase in food intake and a reduction in exercise are obviously two major factors; but experts agreed that other factors must play a part in such an alarming increase in prevalence
Why is less sleep linked with obesity and diabetes?
We now know that the timing, quality and duration of sleep play an important role in neuroendocrine function and glucose metabolism. In fact studies show that sleep restriction results in metabolic and endocrine alterations, including
- decreased tolerance of glucose
- decreased sensitivity to insulin
- increased cortisol levels in the evening
- higher levels of ghrelin - a hunger hormone
- lower levels of leptin which is responsible for satiety (of feeling full)
Let’s look at this in more depth…
What sleep deprivation does to our hormones
The brain is almost entirely dependent on glucose for energy and is the major site of glucose disposal. This means that brain activity changes associated with “sleep-wake” and ”wake-sleep” transitions have a negative impact on glucose tolerance. In fact, glucose tolerance is decreased by more than 40%.
Both ghrelin and leptin concentrations (the hormones directly connected with hunger and with feeling full respectively) are higher during nocturnal sleep than during wakefulness. Therefore less sleep will reduce their effectiveness.
A recent study showed an 18% decrease of leptin levels and a 28% increase in ghrelin when there is sleep deficit. Subsequent questionnaires on hunger and appetite indicated
- a 24% increase in hunger
- a 23% increase in global appetite
- a 32% increase in appetite for high carbohydrate nutrients
These observations would suggest that, where food is readily available, people who are sleep deprived will probably consume an excessive amount of calories particularly in the form of carbohydrates.
The flight or fight hormone Cortisol is designed to stimulate the replenishment of your nutritional stores had you been fighting or fleeing. Unfortunately , the levels of cortisol rises when you are in sleep debt which then contributes to you more hungry and look for foods which give fast energy in the form of sweet, high fat or salty foods.
In combination these misfiring hormones can lead to significant weight gain and an increased BMI which in turn results in insulin resistance, a condition that may promote further weight gain, an increased waist circumference and an increased risk of diabetes.
Unfortunately, up to 20% of overweight and obese individuals also suffer from sleep-disordered breathing or obstructive sleep apnoea which is both independent risk factor for insulin resistance and is known to reduce testosterone in adults and neuroendocrine release and metabolic function in adults and children.
In conclusion it is vital to do all we can to increase our quality of sleep - this means following expert recommendations which include:
- drinking less caffeine
- excluding screen time when going to bed as this stimulates the brain
- finding time for exercise
- striving for a healthy and balanced diet
- spending time outdoors – it has been reported that Vitamin D can have a positive effect on sleep
I hope this has been helpful.
Although every effort is made to ensure that all health advice on this website is accurate and up to date it is for information purposes and should not replace a visit to your doctor or health care professional.
As the advice is general in nature rather than specific to individuals Dr Vanderpump cannot accept any liability for actions arising from its use nor can he be held responsible for the content of any pages referenced by an external link