Get tested first: Cardiologist warns against vitamin D supplements without baseline check

As the days shorten and people spend less time outdoors, the NHS recommendation arrives like clockwork: take a vitamin D supplement from October through March. The logic is sound—the UK's weak winter sun means many people fall short of the nutrient their bodies need. But a cardiologist is pushing back on the assumption that everyone should simply start popping pills when the calendar turns. Dr Osman Najam, a consultant cardiologist, argues that the first step should be a blood test, not a bottle from the pharmacy shelf.

Vitamin D does real work in the body. It regulates calcium and phosphate, which keep bones, teeth, and muscles strong. Without enough of it, children can develop rickets, and adults may suffer from osteomalacia, a condition marked by bone pain and weakness. The nutrient also touches the cardiovascular system—it influences blood pressure, inflammation, and calcium regulation, all of which matter for heart health. The evidence for vitamin D's importance is solid. What remains contested, Najam suggests, is whether most people actually need to supplement.

His argument hinges on a distinction that rarely gets stated plainly: there is a difference between correcting a deficiency and chasing extra protection. If blood work shows your vitamin D is genuinely low, supplementing makes sense. But if your levels are already healthy, taking more does nothing. The excess simply accumulates. Najam has watched people take what he calls "mega doses," convinced that vitamin D will prevent heart disease, cancer, or autoimmune conditions. The evidence for those claims, he says, is thinner than the marketing suggests. Vitamin D is a supporting player, not a cure-all.

The NHS guidance itself is more measured than the supplement industry's promises. Most guidelines suggest adults need between 1,000 and 2,000 international units daily—though individual needs vary. The nutrient is also available through food: fatty fish, egg yolks, fortified milk, mushrooms, liver, and red meat all contain it. Even modest sun exposure helps. Fifteen to twenty minutes outdoors a few times a week, even on cloudy days, can meaningfully boost levels. People with darker skin require longer sun exposure to produce the same amount, a detail often overlooked in generic health advice.

The NHS and local health boards have been consistent in their messaging, though they frame it as a precaution rather than a universal necessity. Nottingham and Nottinghamshire's integrated care board has issued annual alerts recommending that residents consider a daily supplement during the colder months. Dr Dave Briggs, speaking for the health board, noted that low vitamin D can leave people feeling tired, cause aches and pains, and in severe cases soften bones. The board also points out that supplements are cheap and widely available—many pharmacies stock them for just a few pounds, and women and children eligible for the Healthy Start scheme can get them free.

What Najam is really arguing for is a return to basics: test first, then decide. If you are low, supplement. If you are normal, invest your energy elsewhere. He points to the factors that actually move the needle on health—movement, sleep, stress management—and suggests that vitamin D, while important, occupies a smaller corner of that landscape than many people assume. The winter months will still arrive. The recommendation will still come. But before reaching for a supplement, Najam says, know your actual baseline. The test takes minutes. The answer changes everything.