The Daily Mistake That May Contribute to Your Flu

Sleep and the Immune System

Sleeping for fewer hours than necessary every night can adversely affect your health in different ways.

Recent studies have established that sleep is important to optimal functioning of the immune system and sleep deprivation can depress the immune system.

Sleep is an essential part of living and it is during sleep that the body repairs damage and refreshes itself. Certain important physiological, psychological and biochemical processes in the body need sleep. For example, sleep is required for the consolidation of memory and, therefore, learning and other aspects of cognitive function.

While we sleep, the body releases a different set of hormones, neurochemicals, cytokines, and even enzymes. These serve as the clean-up crew to reverse the damage caused by the processes that are important to our waking hours.

Therefore, sleep is an essential balance to wakefulness and the typical adult needs 7 – 8 hours of sleep every night.

When we experience sleep deprivation, the body’s natural balance is thrown out of control. The immune system quickly interprets this as stress and, in truth, sleep deprivation is actually a sign of physical and emotional stress.

Sleep deprivation overworks the immune system and, therefore, leaves it less functional. This can easily allow toxins and infections to override both innate and acquired immunity.

All of these mean that a lack of sleep can increase your chances of getting sick.

The Sleep Study

Researchers from the United Kingdom and the Netherlands demonstrated the negative effect of sleep deprivation on the immune system in a recent study published in the journal, Sleep.

First, they recruited 15 healthy young men and ensured that the participants got 8 hours of sleep at night followed by at least 15 minutes of daylight sun exposure within 90 minutes of waking up. This stabilized sleep schedule was maintained for one week and for the last 3 days, the participants were not allowed caffeine, alcohol or any medications.

Thereafter, the young men were kept awake for 29 hours so that the researchers could study the changes caused by sleep deprivation.

The researchers found that the biggest change caused by the forced sleep deprivation was in the population of a group of white blood cells known as granulocytes.

Ideally, granulocytes follow a day-night rhythmicity that is essential to the role of the immune system in combating toxins and infections. However, the researchers found that sleep deprivation reduced this rhythmic pattern and dramatically increased the number of granulocytes released at night.

The sharp increase in the granulocyte population is a direct immune response to increased stress.

Other studies have also found similar ties between sleep and the immune system. In fact, the fatigue experienced during sickness is one way by which the body tries to sleep because only then can the right immune cells be recruited to fight infections.

Besides hampering the immune system, other negative effects of sleep deprivation include triggering sharp increases in blood pressure and the production of stress hormones as well as inefficient metabolism of glucose.

Sleep Deprivation and the Flu

Can sleep deprivation cause cold and flu? The evidence suggests that it can.

Because lack of sleep diminishes how well and how fast our immune systems can respond to infections, it can increase the odds of coming down with a cold or the flu.

As demonstrated in the study discussed in the previous section, lack of sleep disrupts the normal rhythm of the immune system. Besides affecting the rhythmic activity of granulocytes, other studies have demonstrated that sleep deprivation lowers the population of T cells and increases the production of inflammatory cytokines.

Therefore, the lack of sleep creates the right environment for influenza viruses to flourish. It reduces the ability of the immune system to attack bacteria and viruses and instead promotes inflammation.

Just like stress, lack of sleep increases the chances of falling sick. Therefore, sleeping fewer hours during the flu season increases the odds that you will succumb to cold and flu viruses.

The impact of sleep deprivation on the immune system is also the reason why those who work long hours, especially shift workers, are usually the ones to come down with the flu. By getting fewer hours of sleep, their immune systems respond sluggishly and without coordination.

Sleep Deprivation and Flu Shots

The impact of sleep deprivation on the risk of influenza infection also extends to vaccination. Studies show that sleep deprivation reduces the effectiveness of flu shots.

Experts agree that those who are sleep-deprived take 3 – 4 weeks longer to benefit from flu vaccines than normal sleepers. This observation suggests that lack of sleep weakens the immune system and reduces the number of antibodies produced in response to vaccination.

The changes in the immune system caused by sleep deprivation slow down the response to antigen challenge provided by flu shots.

Because it takes the weakened immune system too long to produce the right antibodies to the flu vaccine challenge, sleep-deprived individuals are likely to still come down with the flu even though they are vaccinated.

The slow response of the immune system to the challenge of flu vaccines can even be dangerous.

It is possible for the antigen introduced in the vaccine to trigger flu-like symptoms since the immune system is already weakened.

In addition, live attenuated influenza vaccines (LAIV) are all the more dangerous because they contain more than viral proteins. Therefore, it is possible that the low viral load meant to stimulate the production of antibodies will present such a huge challenge to the weakened immune system and overwhelm it.

While it seems unlikely that flu shots containing live attenuated viruses can make you come down with flu, it is still possible.

In fact, one human trial found that people who slept for seven hours per night for 2 weeks were three times more likely to come down with colds and flu-like symptoms from rhinovirus vaccines than those who slept for at least eight hours per night during the same period.

Studies on Sleep Deprivation and the Flu

Most studies that have investigated the effects of sleep deprivation on the immune system and influenza have involved mice.

Sleep Deprivation and Immunity to Influenza Viruses

A 1989 study published in the journal, Regional Immunology, provided a close and specific look at the effect of sleep deprivation on the likelihood of influenza virus infection in immunized and unimmunized mice.

For this study, the researchers got two groups of mice. One group remained unimmunized while the second group received two oral immunizations separated by one week.

Then a week later, both groups of mice were challenged with influenza virus intranasally. Some mice in both groups were deprived of sleep for 7 hours as soon as they were infected with the influenza virus while the rest slept normally.

Three days after the viral challenge, the researchers measured the levels of the virus left in the lungs of the mice as well as the levels of antibodies produced by the immune system to combat the virus.

The results of the study showed that

• immunized mice who had normal sleep achieved total clearance of the virus
• immunized mice who were sleep-deprived had the same viral load and antibody level as unimmunized mice
• sleep-deprivation did not affect viral clearance in unimmunized mice

This study supports the theory that lack of sleep increases the chances of coming down with the flu even when flu shots are given.

In addition, the researchers concluded that their results showed that sleep deprivation did not increase the population of the influenza virus but the reduced immune response to the virus.

Other studies also indicate that sleep-deprivation may increase the risk of coming down with flu by affecting the levels of the immunoglobulin antibodies, IgA and IgG.

Can Flu Make You Sleep?

While adequate sleep has been proven to help prevent the onset of the flu, some studies indicate that people affected by the flu sleep more than those uninfected.

A 1995 study published in the journal, Experimental Biology and Medicine, determined whether influenza viral infection altered sleep in a group of mice. First, the researchers recorded the baseline sleep patterns of the mice for 3 days before dividing them into 3 groups.

The first group was infected with the lethal influenza virus, H1N1, while the second group got the non-lethal H3N2 strain of the flu virus in a 10-fold dose of the H1N1 strain. The control group received a placebo in the form of allantoic fluid.

Thereafter, the researchers recorded the sleep pattern of all 3 groups for another 3 days.

The results of the study showed that the mice infected with the lethal strain experienced increased NREM (non-rapid eye movement or “light”) sleep but decreased REM (rapid eye movement or “deep”) sleep.

In addition, the virus reduced the body temperature and physical activities of the mice.

The mice receiving the nonlethal H3N2 strain also experienced a similar change in sleep pattern although to a smaller extent.

The control group, on the other hand, experienced no changes in sleep patterns.

These results show that infection with the influenza virus promotes sleep. In this case, it promoted light sleep and not deep sleep most likely because of the fever and other presentations of the sickness.

However, it is worth noting that it is not the virus that is responsible for the increased sleep but rather the immune system. This means that the immune system tries to defend the body against influenza virus infection by dropping the body’s core temperature, limiting locomotor movement and inducing sleep.

Why would the immune system turn to sleep to combat the flu virus? Because the immune cells needed to combat the virus are released during sleep.

Therefore, sleep may be one of the best medicines to help you overcome a flu attack. This study supports the recommendation to get plenty of rest when you are down with the flu.

Sleep and Vaccination

Sleep is not only a protective mechanism to help the body recruit more immune cells to combat the influenza virus, but it can also increase the success rate of flu vaccines.

In a 2002 study published in the Journal of the American Medical Association, a group of researchers investigated the effects of sleep deprivation on the efficacy of flu vaccination.

For this study, the researchers recruited 2 groups of healthy, young men. While one group was allowed to get normal hours of sleep, the other group was only allowed 4 hours of sleep every night for 4 days. Thereafter, both groups were given flu shots.

Although the control group continued to sleep normal hours, the test group was sleep-deprived for another 2 days before they were allowed to sleep 12 hours per day for 10 days in order to recover.

After the 10^th day, the levels of influenza virus-specific antibodies were measured in both groups.

The results of the study showed that the sleep-deprived group had only half of the antibody level of the control group.

The researchers concluded that sleep deprivation impaired the ability of the immune system to respond properly to the antigen challenge of flu shots. Because antibody production was lower in the sleep-deprived group, they concluded that lack of sleep can reduce the effectiveness of flu vaccines.

This negative effect of sleep on human antibody response is not restricted to flu vaccination.

There is good evidence to indicate sleep boosts the immune system and enhances the antibody protection triggered by antiviral vaccines. A 2003 study published in Psychosomatic Medicine: Journal of Behavioral Medicine showed that sleep improved human antibody response to hepatitis A vaccination.

All of these studies indicate that sleep is more effective than vaccination for the prevention of flu.

While adequate sleep without vaccination can improve your odds of surviving the flu season, vaccination without adequate sleep does not significantly improve your chances of avoiding coming down with the flu.