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The NHS is encouraging millions of Brits to take vitamin D for their wellbeing - but an expert has warned certain warning signs and side effects require attention. An NHS spokesman posted on X: "From October to March we can't make enough vitamin D from sunlight, so to keep bones and muscles healthy, it's best to take a daily 10 microgram supplement of vitamin D. You can get vitamin D from most pharmacies and retailers."

While experts acknowledge that many people across the UK should be supplementing with vitamin D, particularly during winter months, the guidance comes with an important caveat. Sunlight is essential for vitamin D production because UVB rays from the sun initiate a chemical reaction within the skin.

This mechanism transforms 7-dehydrocholesterol into vitamin D3, which plays an iimportant role in calcium absorption, bone health, and supporting the immune system. The UK government advises that everyone should consider taking a daily vitamin D supplement of 10 micrograms (400 IU) throughout autumn and winter, as sunlight isn't sufficiently strong for the body to produce adequate vitamin D, and obtaining enough through diet alone proves challenging.

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Tobias Mapulanga, biomedical scientist and co-founder of Repose Healthcare, has issued a warning about symptoms to look out for. He explained: "As the NHS encourages vitamin D in winter, many people are reaching for bottles in the darker months and accidentally overshooting, then blaming the fallout on seasonal bugs; when constant thirst and needing the loo more often, queasiness, tummy pain or constipation, headaches or brain fog, and new aches or cramps appear soon after increasing your intake or adding sprays or gummies, that points to a supplement backfiring.

"The stakes are clear: the right amount supports you, but doubling up can turn a well-meant routine into feeling worse rather than better." Research revealed that 42% of surveyed UK adults had taken vitamin D supplements within the previous 12 months, yet Which? discovered supplements, including vitamin D, being sold with doses up to 12.5 times the recommended safe upper limit.

NHS England recorded 42 reports over a two-year period of high‐strength vitamin D being administered more frequently than intended, with certain cases requiring hospital treatment for hypercalcaemia, reports Bristol Live.

1. Frequent thirst and urination

Should you discover that you're suddenly experiencing frequent thirst and/or needing the toilet more often after beginning vitamin D supplements, this indicates you might be overdoing it. Reduce your intake to just one 10 microgram tablet and ditch any additional supplements if these warning signs emerge.

Too much vitamin D can throw your fluid and salt levels out of whack, making you feel parched and sending you to the loo repeatedly. Scrutinise food and drink packaging and eliminate multivitamins, sprays, gummies and fortified beverages or cereals containing added D.

Keep water nearby and take regular sips whilst your body readjusts. Remain well below the 100 microgram upper threshold whilst symptoms continue, keep one product by the kettle and stash the remainder somewhere you can't see them.

2. You experience nausea, persistent burping or an upset tummy

Experiencing queasiness, increased burping or stomach upset after taking vitamin D signals something's amiss. Attempt taking your supplement alongside a proper meal and swap from sprays or gummies to a straightforward D3 tablet if problems arise.

Food acts as a buffer for the supplement in your digestive system and minimises irritation, whilst sprays and gummies frequently contain sweeteners or flavourings that don't agree with some individuals. Opt for a basic cholecalciferol tablet with few additives and dial back the dosage to 10 micrograms.

Steer clear of fortified shakes or energy drinks whilst your stomach recovers.

3. Your bones and muscles ache

Should you notice increased bone aches or more frequent muscle cramps when beginning your vitamin D supplement, consider it a warning sign. Reduce your dosage and focus on hydration alongside mineral-rich foods. Excessive vitamin D can disrupt the minerals that muscles depend upon, whilst dehydration increases cramping likelihood.

Consume a large glass of water with meals and incorporate yoghurt, leafy greens, beans and bananas throughout the day. Gentle stretching and a brief walk help alleviate stiffness.

Return to a single 10 microgram dose and avoid any additional supplements whilst symptoms subside.

4. You can't think straight

Mental fog and headaches are clear warning signs that your vitamin D consumption is excessive. Replace any multivitamin or high-strength product with a straightforward 10 microgram D3 tablet.

Elevated doses can increase calcium levels, whilst additives in multivitamins can cloud thinking. Select a product containing only cholecalciferol and basic bulking agents.

Take it with food at the same time daily to maintain steady intake and be gentler on the digestive system. Leave combined A+D products on the shelf and concentrate on one simple D3 tablet.

Choose a small tablet to make consistency effortless. Finally, keep tabs on how many items you're taking that include vitamin D, as it's entirely possible to have too much without realising. Check all sources and select just one daily item to prevent doubling up from tablets, multivitamins, sprays, gummies and enriched foods.

Spread out everything containing vitamin D and scrutinise each label thoroughly. Convert IU to micrograms by dividing by 40 so totals are obvious at first sight.

Bin the extras and stick to just one 10 microgram source. Note down the amount and any thirst, regular weeing, stomach problems, cramps or mental fogginess to identify connections with your intake.