Winter in the UK is a particular kind of test for the immune system. Sunlight is thin, central heating dries out airways, and we spend a lot more time indoors with other people's germs. A few sensible habits make most of the difference.
Sleep is the foundation
Most immune work happens overnight. Adults who get fewer than six hours' sleep are roughly four times more likely to catch a cold than those who get seven or more. If you only fix one thing this winter, fix bedtime.
Vitamin D, the obvious gap
From October to March, UK sunlight isn't strong enough to make meaningful vitamin D in the skin. Public health guidance is straightforward: most adults benefit from a daily supplement during the winter. A good multivitamin usually covers it.
Eat the rainbow, literally
Citrus, peppers, kiwi, broccoli, berries — colour on the plate generally means antioxidants. Add fermented foods like yoghurt, kefir or sauerkraut for the gut, which does a quarter of your immune work.
Move, but don't punish
Moderate exercise gives immunity a boost. Hammering yourself with two-hour gym sessions when you're already run-down does the opposite. A daylight walk most days is more useful than a hero session twice a week.
The small details
Hydrate, even though you're not thirsty. Keep one window cracked. Take your multivitamin with the same meal each day so you don't forget. None of it is dramatic; all of it adds up.