Surprising things that do (and don't!) affect your immune system

Between cold and flu season and the COVID-19 pandemic, many people are trying to keep their immune systems as healthy and strong as possible.

Here are factors that do impact your immune system, and other factors that, contrary to popular belief, have little or no effect on your body’s ability to combat an infection.

Things that do affect your immune system

1. Sleep

People who get less than 7 hours of sleep a night are more likely to contract an infection when they’re exposed to a virus compared to their well-rested counterparts. When they do get sick, it takes sleep-deprived people longer to recover from the infection than people who get more sleep.

It’s recommended that adults get 7-9 hours of sleep each night to keep their immune system as healthy as possible.

Sleep is vital to immune system health because while you’re asleep, your body produces proteins called cytokines that your immune system needs to combat infections. When you don’t get adequate quality or quantity of sleep, your body’s production of cytokines is diminished, making you more prone to infection.

Because sleep is so important to your immune system, it’s wise to develop bedtime habits that help promote a healthy quality and quantity of sleep every night.

Also, it’s important to consult a medical professional if you’re experiencing insomnia, sleep apnea, or other conditions that interfere with your ability to get a good night’s sleep.

2. Cold temperatures

You’re more likely to get sick in cold temperatures than in warmer temperatures for several reasons.

First, many viruses are more active in cold temperatures. This is one of the reasons why cold and flu season occurs in the winter each year, and why rates of COVID-19 increased in the late fall and early winter of 2020.

Cold temperatures also cause blood vessels to constrict. When this happens, your respiratory tract gets fewer white blood cells that it needs to ward off respiratory infections like influenza and bacterial pneumonia.

Another reason why you’re more likely to get sick in cold temperatures is that you’re probably spending less time outdoors, which can result in a drop in your Vitamin D levels. Your body’s immune system needs Vitamin D to function properly, so getting sunshine, taking a Vitamin D supplement, or incorporating Vitamin D-rich foods into your diet are all useful wintertime strategies to stay as healthy as possible. Vitamin D helps against the risk of complications of infection. In COVID-19 it prevents an exaggerated inflammatory response that has been known to cause severe complications and an increased risk of death.

Finally, there’s also research to suggest that your immune cells are more sluggish in cold temperatures than in warmer temperatures, which is why feeling cold or spending time in cold weather is more likely to make you sick.

3. Stress

Stress is another factor that’s proven to weaken your immune system. When you’re stressed, your body releases increased levels of cortisol, a stress-induced hormone.

This hormone suppresses lymphocyte production, which means that when you’re stressed, you have fewer white blood cells circulating in your body, and you’re more prone to contracting an infection.

In addition, stress also often causes insomnia. Sleep deprivation combined with high cortisol levels will make you more susceptible to infection.

Things that don’t affect your immune system

1. Wet hair

Chances are that when you were a child, a grown-up warned you that if you went outside with wet hair, you would catch a cold.

Wet hair in and of itself does not increase your chances of getting sick. It doesn’t attract viruses to you, and it doesn’t have any effect on your respiratory tract or immune system.

Indirectly, though, going outside with wet hair when it’s outside may play a role in lowering your body temperature, which can lower the activity of your immune system. So, in cold weather, it’s probably a good idea to dry your hair before you go outside and cover your head with a hood or hat to keep your body heat from escaping into the surrounding air. Even though it’s tempting to take a long, hot shower after spending time outdoors in cold weather, this contributes to dry skin and corners of lips cracked.

2. Supplements

Another commonly held belief is that consuming a large number of supplements like Vitamin C, zinc or echinacea protects people from getting sick -- or, if they do get sick, helps them recover faster.

There is little evidence that increasing your intake of these supplements is beneficial. In some cases, it’s harmful because your body has to work overtime to metabolize what you ingest, and these supplements can have unintended consequences.

For example, since Vitamin C is processed by your kidneys, taking too much Vitamin C can cause kidney damage. Nasal sprays that contain zinc have caused patients to permanently lose their sense of smell since zinc is a heavy metal that can deposit on the olfactory nerve.

Patients who are deficient in a vitamin or mineral do benefit from taking a supplement that brings their level up to normal. But for patients who are not deficient in a vitamin or mineral, consuming excess amounts has not been proven to be effective, and it may do more harm than good.

3. Fever-reducers

Many people are under the impression that taking a fever-reducer diminishes their body’s ability to ward off infection.

Fevers happen when the hypothalamus, the body’s “thermostat” in the brain, raises the body’s temperature in an attempt to make the environment less hospitable to a pathogen. Since most viruses are more active at lower temperatures, raising the body’s internal temperature is one mechanism your body uses to fight infection.

While running a low-grade fever may be harmless, running a high fever, especially for a prolonged period, can cause dangerous complications.  A high fever can lead to dehydration because fluid evaporates off hot skin faster than cooler skin. In children under five years old, a rapid temperature rise can also cause a febrile seizure.

Using an over-the-counter fever-reducing medication like ibuprofen can often help prevent fever-related complications and reduce uncomfortable symptoms like headaches and body aches. And there’s no evidence to show that using a fever-reducer has a negative effect on your immune system’s ability to fight infection.


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Written by Sarah Thebarge, Physician Assistant