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

As the days shorten and people spend less time outdoors, the question of vitamin D supplementation becomes routine. The NHS recommends that nearly everyone consider taking a daily supplement between October and March, a straightforward piece of seasonal health advice. But a London cardiologist is asking people to pause before they reach for the bottle—and to get tested first.

Dr Osman Najam, a consultant cardiologist, has been posting on social media about what the actual evidence shows regarding vitamin D and heart health. His core message is simple: vitamin D deficiency is real, particularly in the UK where sunlight is scarce for much of the year. The vitamin plays a genuine role in the body, regulating calcium and phosphate levels that keep bones, teeth, and muscles strong. Without enough of it, children can develop rickets and adults can suffer from osteomalacia, a painful softening of the bones. The cardiovascular connection is real too—vitamin D affects blood pressure, inflammation, and calcium regulation, all of which matter for heart health.

But here is where Najam's advice diverges from the standard recommendation. He argues that supplementation only makes sense if you are actually deficient, confirmed by a blood test rather than guesswork. If your levels are already healthy, he says, taking more vitamin D provides no additional protection. It simply accumulates in your system without benefit. Most guidelines suggest that adults need between 1,000 and 2,000 international units daily, though individual needs vary based on baseline levels. The problem Najam identifies is that people often take much larger doses, believing vitamin D is a preventive cure-all for heart disease, cancer, and autoimmune conditions. The evidence for those claims, he notes, is weaker than popular belief suggests.

What gets overlooked in the supplement conversation, according to Najam, is that vitamin D is available from food sources—fatty fish, egg yolks, fortified milk, and other products—and from modest sun exposure. Even 15 to 20 minutes of sunlight a few times a week makes a measurable difference. The real issue, he argues, is not vitamin D alone but the broader picture of health. Movement, sleep, and stress management move the needle far more than megadoses of a single nutrient. Vitamin D is important when you lack it, but it is a supporting player in health, not the star.

The NHS position remains that everyone should consider supplementation during winter months. Nottingham and Nottinghamshire's health board has issued annual reminders, noting that low vitamin D can cause fatigue, aches, and bone softening. The board recommends discussing dosage with a pharmacist and notes that low-cost supplements are widely available, with free options for women and children who qualify for the Healthy Start scheme. Beyond supplements, the health board advises spending time outdoors—even 30 minutes daily on cloudy days helps—and eating vitamin D-rich foods including oily fish, liver, mushrooms, red meat, cheese, and fortified spreads and cereals. People with darker skin require longer sun exposure to produce the same amount of vitamin D as those with lighter skin, a detail often missing from generic health guidance.

The tension between Najam's advice and the NHS recommendation is not really a conflict. Both agree that vitamin D matters. The difference lies in the starting point: the NHS recommends supplementation as a precaution for everyone during winter, while Najam argues for testing first to know whether you actually need it. For someone heading into the darker months, the practical step is clear—get a baseline measurement before October arrives, then decide whether a supplement belongs in your routine or whether food and sunlight will suffice.