When a cold hits and your energy is at its lowest, it’s tempting to reach for tea, juice, or sports drinks. Yet according to doctors, there’s one option that’s far more effective.
During illness, the body loses large amounts of fluid through sweating, fever, vomiting, or diarrhea.
At the same time, metabolic demands increase as the immune system works overtime.
Sports medicine physician Mariam Zakhary explains that maintaining proper hydration is essential for recovery speed.
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Dehydration can worsen symptoms, thicken mucus, and reduce circulation, making it harder for the body to fight infections.
A similar conclusion comes from Dr. Matthew Heller, a family medicine physician and professor, who notes that fluid requirements rise significantly when sick.
Insufficient hydration, he says, can disrupt immune response, digestion, and temperature regulation.
The hidden effect on the immune system
A 2025 study published in Physiological Responses to Psychosocial Stress found that inadequate fluid intake can raise cortisol levels, a stress hormone that weakens immune function.
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Likewise, a 2024 iScience study showed that dehydration can disturb gut microbiota and reduce immune cell counts.
According to Mariam Zakhary, proper hydration promotes a stable gut environment and stronger immune defenses.
Water also plays a central role in transporting nutrients, oxygen, and immune cells through the bloodstream.
Maintaining sufficient blood volume ensures that the body’s defenses reach infection sites efficiently.
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It also supports kidney function by flushing out waste and inflammatory byproducts produced during illness.
The simple solution
What seems most basic often proves most powerful. Doctors agree that plain water is the best drink when you’re sick.
It stabilizes hydration, supports the immune system, prevents muscle cramps and constipation, and helps regulate body temperature.
Even mild dehydration can negatively affect mood, concentration, and short-term memory.
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Experts therefore recommend sipping water frequently in small amounts rather than drinking large glasses at once.
For those who find plain water unappealing, a touch of lemon or honey can make it easier to drink.
The worst drink
According to WebMD, alcohol is one of the beverages best avoided during illness.
It causes dehydration and can worsen symptoms such as nausea, headaches, and body aches.
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It also impairs the body’s ability to fight infections by weakening immune function. Doctors recommend waiting until full recovery before consuming alcoholic drinks.
This article is based on information from Real Simple, Physiological Responses to Psychosocial Stress, iScience og WebMD.