Experts are warning that seemingly minor discomfort following vitamin D supplementation could signal a potentially serious imbalance within the body. The caution comes as vitamin D supplements remain widely used to address a global deficiency, but also as reports of adverse reactions surface.
According to Morgan Walker, a registered dietitian, the most common cause of feeling unwell after taking vitamin D is elevated calcium levels in the blood. “Vitamin D is fat-soluble and plays a crucial role in regulating calcium absorption,” Walker explained in statements to Verywell Health. “When taken in high doses over extended periods, or even moderate doses in sensitive individuals, calcium levels can rise, leading to a range of unpleasant symptoms.”
These symptoms include nausea, constipation, fatigue, muscle weakness, headache, increased thirst and frequent urination. A feeling of “brain fog” has also been reported. In severe cases, irregular heart rhythms or kidney problems can occur. Walker also noted that a magnesium deficiency can exacerbate the issue, as the body requires magnesium to metabolize vitamin D effectively. Insufficient magnesium can manifest as muscle cramps and sleep disturbances.
However, discomfort immediately after taking a supplement may not always be due to vitamin D itself, Walker cautioned. Sensitivity to other ingredients in the supplement, such as the oils used in the capsules – including soybean, coconut, or corn oil – could be the culprit.
Walker advises individuals experiencing these symptoms to temporarily discontinue the supplement and undergo blood tests to assess their vitamin D levels and related mineral balances. She strongly recommends against exceeding the daily dose of 4,000 international units (IU) without medical supervision, warning that exceeding this amount increases the likelihood of side effects.
Alternative methods of obtaining vitamin D exist, including dietary sources. Fatty fish like salmon, mackerel, and sardines are naturally rich in vitamin D3, the form most readily absorbed by the body, according to Walker. Other food sources and sunlight exposure can also contribute to maintaining adequate vitamin D levels. Exposure to sunlight allows the body to produce vitamin D when skin is exposed to ultraviolet rays, providing approximately 80 percent of the body’s needs, according to research.