Why Do People Get Sick in the Winter?

colds cytokines flu holiday blues holiday overindulgence holidays immune system infections inflammation melatonin respiratory system sunlight uv radiation viruses vitamin d white blood cells winter Nov 09, 2024

in the cold and snowy outdoors, a woman in winter clothes dabs at her nose with a tissue.

The leaves are changing color, and the days are getting shorter and colder. With winter around the corner, snowy landscapes and warm beverages by the fireplace may come to mind — and you may also expect an increased risk of colds and the flu. But are you really more prone to illness in the frosty months? The short answer is yes, for a variety of reasons including:

Cold, dry winter air
The effect of limited sunlight
Viruses thrive in winter
More time indoors
The impact of holiday festivities

Let’s begin by exploring how breathing in chilly winter air can lower your defenses against viruses.

Cold, dry winter air

Respiratory viruses enter your body mainly through your nose. Upon the germs’ entry, your nose releases billions of extracellular vesicles (EVs) into your nasal mucus. These tiny vesicles try to fight off the viruses before they can invade your body further.¹

But studies show that cold air substantially lowers your nose’s production of EVs. As a result, viruses can more easily bypass your nasal defenses and infect the rest of your body.²

What’s more, dry air — which comes with lower temperatures — impairs the mucus secretion in your nasal lining. This means your nose becomes less efficient at trapping germs and stopping them from entering your body.³

The effect of limited sunlight

Soaking up the sun is the most natural way to get enough Vitamin D. Crucial for strong immunity, Vitamin D enhances your immune cells’ ability to produce infection-fighting proteins. In the winter though, the amount of available sunlight is much more limited. So, your immune system becomes compromised, and you become more vulnerable to colds, flu, and other illnesses.^4,5

The effect of sunlight on your health goes beyond Vitamin D. Your eyes’ exposure to sunlight signals your brain to reduce melatonin production. If you’ve noticed you feel like sleeping more in the winter, this might be why. Melatonin is a powerful hormone that regulates your sleep-wake cycle, and also plays a role in your immune defenses.⁶

Less sunlight in the winter means your brain produces more melatonin, even during the day. But research suggests that high melatonin for long periods hinders cytokine production. Cytokines are signaling molecules that coordinate your immune responses. Because of their regulatory role, it’s important not to have too many or too few cytokines. Not having enough cytokines can make your immune response less effective, while having too many can kill you (cytokine storm). Large amounts of melatonin can also impair the white blood cells that fight infections and kill tumors.^7,8

Viruses thrive in winter

Most respiratory viruses have an outside layer called the envelope. This layer, which protects the viruses’ genetic material, consists mainly of lipids (fats). Within a certain range, low temperatures stabilize the envelope by making the lipids more rigid. In addition, cold temperatures disable various enzymes in the environment that could break down viral envelopes.⁹

Also, dry air in winter contains fewer water molecules. This means there are fewer particles that could hinder the movement of virus-containing droplets — which you release by coughing and sneezing — through the air. On top of that, dry air makes the droplets lose water and become smaller and lighter. So, viruses can stay in the air longer and spread from person to person with greater ease.⁹

Lastly, the lower angle of sunlight during the winter months means less intense UV radiation. UV rays inactivate viruses by destroying their genetic material. So although you’re less likely to get sunburned in the winter, the wintertime sunlight isn’t as effective at protecting you from viruses.⁹

More time indoors

As temperatures drop, you probably find yourself spending more time indoors. Although enclosed spaces may help you keep warm, they can expose you more to illness-causing germs. This is because indoor spaces often have poorer ventilation, allowing viruses to linger longer in the air.¹

Plus, indoor spaces typically have surfaces prone to contamination — for example, doorknobs, tabletops, light switches, and sink faucets. Someone infected with a virus can deposit it directly on these surfaces by touching them. It’s also possible for viruses in the air to settle onto the surfaces on their own. Once you touch a contaminated surface, you can get infected too, especially if you touch your face afterward.^1,10

On top of that, viruses on surfaces can get carried back to the air. This can happen through activities like opening the curtains, walking across the room, or vacuuming the floor. Such resuspension further contributes to the spread of viruses in indoor environments.¹⁰

The impact of holiday festivities

In many parts of the world, the winter months coincide with an extended holiday season that may last for as long as two months leading up to the New Year. But the hustle and bustle of the holiday season often poses an extra challenge to your health.

During the holidays, you may find yourself shopping for presents in crowded stores. You might attend or even host parties. Perhaps you’ll even feel pressured to spend time with difficult relatives or colleagues. These activities – demanding time, money, and patience – can increase your stress levels a lot. And all that stress reduces your infection-fighting white blood cells, making you more vulnerable to illness. What's more, busy holiday schedules prevent many people from getting enough sleep and exercise. The lack of these things further harms your immunity.^11,12,13,14

Lastly, holiday gatherings often tempt you to indulge in decadent foods and drinks. These treats typically abound with sugar, alcohol, and other dietary triggers for immunity-lowering inflammation. This effect will be in play even if you’re reading this article from a part of the world where it’s summer during the holidays.^15,16

Conclusion

Weather conditions, viral biology, hectic schedules, and unhealthy tendencies — all these factors can add up to weaken your immunity and make you more likely to get sick in the winter.

Holiday stress and overindulgence are among the biggest contributors to getting sick in the winter. But the good news is, you can break the cycle! Don’t miss the chance to create a sustainable, health-focused lifestyle this holiday season and beyond. Sign up for the Healthy Happy Holidays workshop here.

References

Why Do People Get Sick in the Winter?

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