You’ve likely heard about how sleep is crucial to your health. Studies have shown how sleep deprivation can contribute to obesity by decreasing levels of the hunger hormone leptin and elevating the hunger hormone ghrelin. It can raise the risk of developing high blood pressure, heart disease, and stroke. Sleepiness raises the risk of having a car accident and it impairs attention, alertness and concentration, making it difficult to learn new information. It raises your risk of developing depression and anxiety and it ages you, too.
An October 2016 study suggests that shortened sleep can also impair your immune system.
Sleep is a time when a number of crucial body functions occur. One of those important functions involves the levels of circulating T cells. T cells are lymphocyte cells produced by the thymus gland that actively participate in the body’s immune response. They are the foundation of the human body’s immune system.
T cells hunt down and destroy cells that are infected with germs, or cells that have become cancerous. They also help to activate and help other immune cells that ingest germs or that make anti-infection cells called antibodies. T cells also have "memory" and recognize a germ that they have encountered previously.
Large numbers of T cells routinely circulate in the blood stream, poised to attack invaders. We know that even during the deep phases of sleep, the body can release T cells, along with other chemical messengers, to fight invading germs.
Researchers wanted to assess how lack of sleep affects the immune system. Fourteen men (average age, 25) were recruited to participate in two separate studies. The duration of each study was 24 hours, 8 AM to 8 PM. In one study the subjects slept from 11 PM to 7 AM. In the second study, they were kept awake for the entire 24-hour cycle. Blood studies were done at different intervals during the two studies.
In the group that was allowed to sleep, T cell levels showed a reduction within three hours of falling asleep. In the second study, when the subjects remained awake, T cell numbers remained high. The bloodwork did not show where the T cells went since it’s not possible to follow their migratory patterns. The researchers did reference prior studies that suggested that these T cells may accumulate in lymph nodes, where they remain at unusually high levels.
This study confirms that T cell levels follow a circadian rhythm with peak levels high before sleep and then a rapid decline during the early hours of sleep. The findings also suggest how sensitive T cell levels are to lack of sleep. The study confirmed the notion that if you are considering a vaccine like the flu vaccine, you want to get the injection after a good night’s sleep so that your T cell levels and your immune system are optimal.
Another crucial observation is the concept of the low T cell levels during sleep, a time when stress levels are typically low and when onslaught from invading pathogens is lower. If you are chronically sleep deprived, those high T cell levels will persist and may impair the function of the T cells at the very time you need them to arm and attack, i.e., when a true invasion of germs or cancer occurs.
As a physician who specializes in sleep medicine, it’s become obvious to me that sleep hours and quality need to be a regular part of the discussion I have with my patients, even when they come in for other complaints. Sleep affects many crucial body functions and can have significant health consequences when it is shortened or of poor quality. It may be time to consider sleep as another “vital sign,” and when a patient has height, weight, respiration and pulse taken, as well as blood pressure, a few sleep screening questions should be asked, as well.