Immune & Respiratory

What connects these conditions

Colds, flu, coughs, sore throats and sinus problems are mostly viral. That one fact determines almost everything useful about how to handle them.

Antibiotics do nothing against viruses. Taking them anyway does not shorten your illness and does contribute to resistance, which is why doctors decline to prescribe them for a cold and why that refusal is good medicine rather than an oversight.

What the evidence supports

• Sleep. The best-supported thing on this list. People who sleep under six hours are several times more likely to catch a cold after exposure than those sleeping seven or more.
• Zinc, started early. Zinc lozenges taken within 24 hours of symptoms starting can modestly shorten a cold. Started on day three, they do nothing.
• Vitamin C, taken regularly. It does not prevent colds in the general population, but regular intake slightly shortens them. Taking a large dose once you are already ill does very little.
• Vitamin D if you are deficient. Correcting a deficiency reduces respiratory infections. Taking more when you are already replete does not.
• Fluid and rest. Unglamorous, and the things that actually help.

What does not work

"Immune boosting" is not a real mechanism. An overactive immune system causes autoimmune disease; you do not want it boosted. What you want is an immune system functioning normally, which means adequate nutrition and sleep — not a supplement.

Most products sold as immune boosters are vitamin C and zinc at doses you could get from food, priced considerably higher.