Cardiologist warns: Get tested before taking vitamin D supplements this winter

As the days shorten and the sun retreats behind British cloud cover, the NHS will soon recommend that most people start taking vitamin D supplements. It's a seasonal ritual, backed by public health guidance that runs from October through March. But one cardiologist is asking people to pause before they reach for the bottle.

Dr Osman Najam, a consultant cardiologist, has been making the case on social media that the real question isn't whether to take vitamin D—it's whether you actually need it. The vitamin, often called the sunshine vitamin, does genuine work in the body. It regulates calcium and phosphate levels, which keep bones, teeth, and muscles functioning properly. Without enough of it, children can develop rickets, and adults can suffer from osteomalacia, a condition marked by bone pain and weakness. The deficiency is real, particularly in the UK, where winter sun is scarce and people spend less time outdoors.

What Najam is pushing back against is the assumption that everyone should supplement, and that more is always better. He points out that vitamin D matters for heart health—it affects blood pressure, inflammation, and calcium regulation, all factors that influence cardiovascular function. But that doesn't mean taking a supplement will prevent heart disease or cancer, despite what many people believe. "The evidence for those claims is weaker than people actually think," he says. His core argument is simple: get tested first. If you're genuinely deficient, supplementation makes sense. If your levels are already healthy, taking more provides no extra protection.

The NHS guidance itself is more measured than the supplement industry's marketing suggests. Most guidelines recommend between 1,000 and 2,000 international units daily for adults, though individual needs vary. Najam emphasizes that people often overlook the other ways to maintain adequate vitamin D. Fatty fish, egg yolks, fortified milk, and mushrooms all contain it. Even modest sunlight exposure—15 to 20 minutes a few times a week—helps the body produce it naturally. The problem Najam observes is that people take what he calls mega doses, imagining they're building a shield against multiple diseases, when the actual benefit is much narrower: vitamin D supports normal function when you're deficient, nothing more.

The NHS guidance from Nottinghamshire's health board acknowledges this layered approach. Dr Dave Briggs has advised that low vitamin D can leave people feeling tired, with aches and pains, and can soften bones over time. The recommendation to consider supplementation between October and April stands. But the guidance also notes that sunlight exposure—even 30 minutes daily, even on cloudy days—can help. For people with darker skin, who require longer sun exposure to produce the same amount of vitamin D as those with lighter skin, this matters particularly. Pharmacists can discuss appropriate doses, and low-cost supplements are widely available; women and children qualifying for the Healthy Start scheme can access them free.

Najam's final point reframes the whole conversation. Vitamin D is a supporting player, not the star. If you're low, supplement. If you're normal, the things that actually move the needle are movement, sleep, and stress management. Before the season turns and the supplement bottles appear on pharmacy shelves, he's asking people to do one thing first: find out where they actually stand.