In recent years, NHS doctors have highlighted the benefits of vitamin D for overall health, particularly during the colder months when sunlight is limited. The vitamin plays an important role in regulating calcium and phosphate levels in the body, helping maintain strong bones, teeth, and muscles while preventing conditions such as rickets and osteomalacia. Because sunlight is the body’s main source of vitamin D, people living in the northern hemisphere often struggle to get enough during winter.

For this reason, the NHS recommends that adults consider taking a daily vitamin D supplement of around 10 micrograms between October and March. However, health experts warn that these supplements should still be taken carefully. Some people may experience negative effects if they take more than their body needs. According to biomedical scientist Tobias Mapulanga, increasing vitamin D intake too quickly or combining multiple supplement types can sometimes lead to unwanted symptoms.

One possible warning sign is constant thirst and frequent urination, which can occur when vitamin D affects fluid and salt balance in the body. Nausea or stomach discomfort may also appear, especially if supplements contain additives that irritate the stomach. Some people may also notice muscle cramps or unusual aches, as excessive vitamin D can disrupt mineral levels needed for proper muscle function. Another reported symptom is difficulty concentrating or “brain fog,” which may be linked to increased calcium levels caused by high doses.

Experts recommend sticking to the advised dosage and taking supplements with food if needed. According to the NHS, adults should not take more than 100 micrograms (4,000 IU) per day, as excessive amounts over time can lead to calcium buildup in the body, potentially harming bones, kidneys, and the heart. As with any supplement, moderation and medical guidance are key to staying safe.