When Weather Changes, Let Vitamin C Help You

Vitamin C is an essential nutrient that contributes to the normal function of the immune system, and because the body neither produces it nor stores much of it, the supply has to be renewed daily. Quercetin and citrus bioflavonoids are plant compounds frequently formulated alongside it, though the evidence on them is still developing: the largest trial to date, in 1,002 adults, found no overall difference from placebo.

What changing weather actually does

Swings in temperature and humidity dry out the nose and airways, and fine particulate matter such as PM2.5 irritates the eyes, nose and throat. Add crowded indoor spaces and less sleep, and it becomes a season when people feel less resilient.

What vitamin C does

Vitamin C contributes to the normal function of the immune system, to normal collagen formation, to protection of cells from oxidative stress and to normal energy-yielding metabolism. It also improves absorption of iron from plant foods, and requirements are somewhat higher in smokers.

What is usually formulated with it

• Acerola cherry and rosehip: two of the most vitamin C-dense fruits, used as naturally sourced raw materials.
• Citrus bioflavonoids: the flavonoid fraction occurring alongside vitamin C in citrus fruit.
• Quercetin: a flavonol found in onions, apples and tea, studied for antioxidant activity.

What the largest quercetin trial found

The study most often cited here appeared in Pharmacological Research in 2010: a randomized trial in 1,002 adults aged 18 to 85 taking quercetin or placebo for 12 weeks, with upper respiratory illness tracked by questionnaire. Across the whole group there was no significant difference from placebo. An exploratory subgroup analysis among older, physically fit participants reported fewer total illness days, which the authors described as needing confirmation.

The everyday basics matter most

Handwashing, adequate sleep, hydration, a mask on high-dust days and staying home when unwell do more than any supplement. A varied diet covers vitamin C for most people, and a supplement keeps that intake steady rather than replacing it. Check with a doctor or pharmacist first if you are pregnant, breastfeeding or on prescription medicines.