Nutrition experts warn that feeling unwell or experiencing pain after taking vitamin D supplements may indicate an imbalance of elements in the body, despite the widespread use of these supplements to treat the globally prevalent deficiency. As nutrition specialist Morgan Walker explained to Very Well Health, the most common cause of these symptoms is high calcium levels in the blood, as vitamin D is fat-soluble and plays a key role in regulating calcium absorption. When taking high doses for long periods, or even moderate doses in some sensitive individuals, calcium levels can rise, causing unpleasant symptoms. Signs of high calcium include nausea, constipation, fatigue, muscle weakness, headache, increased thirst and urination, as well as what is described as "brain fog." In severe cases, heart rhythm disorders or kidney problems may occur. Walker also noted that magnesium deficiency can worsen the issue, as the body needs it to metabolize vitamin D, and its lack can lead to symptoms like muscle cramps and sleep disturbances. He added that feeling unwell immediately after taking a supplement could be due to sensitivity to components other than the vitamin itself, such as the oils used in capsules, like soy, coconut, or corn oil. He advised to temporarily stop taking the supplement if symptoms appear and to get blood tests to check the vitamin and related element levels. Walker emphasized that the daily dose should not exceed 4000 IU without medical supervision, warning that excessive intake increases the likelihood of side effects.
