For the most part, it’s very unlikely you’ll experience any problems from side effects with vitamin D. Even the most common issues present in less than one in 100 people, and in many of these cases it occurs when the recommended dose has been exceeded.
The most common side effects are hypercalciuria, which is too much calcium in the urine, and hypercalcemia, which is too much calcium in the blood.
Hypercalcemia is a dangerous condition that needs immediate medical attention. Symptoms are constipation, loss of appetite, headaches, confusion, depression, excessive thirst, abdominal pain, tiredness and muscle pain.
Allergic reactions are rare, but it’s important that you know what to look for in case they do present. If you notice any of the following, seek immediate medical attention: swollen lips, mouth, throat, face, severe itching, hives and difficulty breathing.