You go to a doctor with a complaint. He sends you for a test. Based on the test result he makes a diagnosis and prescribes treatment. Diabetes? Check your blood glucose. Hypertension? Check your BP. Kidney disease? Check your creatinine. But what if you are sleep deprived? Is there a test your doctor could order to measure how sleep deprived you are? No, there is not! At least, not yet.
Sleep deprivation, apart from short term effects on brain function, increases the risk of many diseases, from diabetes to dementia. And yet, we have no objective measure of sleep deprivation! The best we can do is administer a questionnaire that captures subjective measures of the effectiveness of sleep. While these questionnaires may serve a purpose, they are nowhere close to being precise enough to pinpoint where the problem lies – do we have sufficient deep sleep, is our sleep consolidated or fragmented, how many times did we wake up, how much sleep will we need to catch up on sleep we have lost, etc. Even worse, these questionnaires do not address the issue of functional consequences of sleep deprivation – for example, ‘how has our liver metabolism been affected?’ or ‘how much waste is clogging up the brain due to lack of sleep?’.
Given the powerful impact sleep has on health, physicians should make sleep a part of their discussion with patients along with diet and exercise. If they choose to have such a discussion they have to resort to asking for a detailed sleep history. Sleep quantity can be reported on by patients by maintaining a diary of when they went to bed and when they woke up. But sleep quality is a critical variable that they have no objective measure of other than the subjective feeling of freshness when they awaken. Without such actionable test results, doctors lack the context to advise on sleep and avoid the topic altogether.
Another scenario where an objective test for sleep deprivation could prove useful is in the transportation industry. Drivers who have not slept for more than 17 hours can be as impaired as someone who is legally drunk. While we have simple breathalysers that can measure blood alcohol, there is no test for sleep deprivation that police officers could use at road stops. It is therefore not surprising that sleepy drivers are a major cause of accidents.
The gold standard tool for assessing sleep is a polysomnography study that tracks multiple parameters over a sleep session. Polysomnography studies are carried out in specialised sleep laboratories and are expensive and time-consuming and therefore not suitable for daily use.
While it is desirable to have a simple blood test to measure sleep deprivation, we must remember that sleep is a complex behaviour orchestrated by an even more complex organ – the brain. It is simplistic to assume that it will yield its secrets so easily and that a simple blood test will ever provide enough information to provide an actionable diagnosis. A whole battery of tests is more likely to be required to assess sleep comprehensively.
Until we have objective tests for sleep deprivation, we have to rely on the technology available to us today. Smartwatches and fitness bands are designed to provide information on sleep by tracking movements. The algorithms that drive these devices have evolved sufficiently to make them reasonably reliable sleep trackers. Other than these gadgets the best measure of sleep we have today is how we feel when we wake up in the morning. Even if our subjective feeling does not pinpoint with precision the physiological alterations experienced during disturbed sleep it remains a reliable indicator of the overall quality of our sleep. And if in the morning our subjective feeling tells us we have not slept well, then we should consider that sufficient feedback from our body and focus on measures that will help us sleep better. The immeasurable darkness of sleep need not be a barrier between us and good sleep!