The "sunshine vitamin," vitamin D, carries potential dangers when taken in excess, scientists warn. While a deficiency poses health risks, an overdose can be toxic, particularly for vulnerable populations.

Excessive vitamin D intake elevates calcium absorption, leading to hypercalcemia. This condition can cause dangerous calcium deposits in arteries and soft tissues, increasing the risk of kidney stones, disrupting bone metabolism, and triggering symptoms like nausea, vomiting, fatigue, and bone pain.

While most individuals recover after discontinuing supplements and receiving treatment to lower calcium levels, severe cases can result in kidney failure requiring dialysis or fatal intestinal bleeding.

Concerns are growing over "considerable complacency" regarding vitamin D's toxic potential. The exact amount considered "too much" remains debated, but a surge in vitamin D interest, fueled by popular claims, has coincided with an increase in toxicity cases.

Vitamin D is primarily produced by the body through sunlight exposure, with a smaller portion obtained from dietary sources like fatty fish. Its roles include aiding calcium absorption, supporting immune function, and maintaining cell growth and metabolism.

However, the effectiveness of vitamin D supplements is controversial, with some studies suggesting benefits in areas like aging and cognition, while others cast doubt on their efficacy. The risks associated with supplements are significant, often stemming from errors in dosage or treatment for deficiency.

Cases of vitamin D toxicity are increasing, with a significant rise reported in the US between 2000 and 2014, involving both children and teenagers. While fatalities were not recorded during this period, serious medical outcomes did occur.

Health experts advise caution, recommending daily intake typically not exceeding 15-20 mcg (600-800 IU) unless medically advised, and avoiding more than 100 mcg (4,000 IU) daily, considered the safe upper limit. Consulting a medical professional before starting or stopping any supplement is crucial.