High-Dose Vitamin D Supplements... A Silent Threat to Kidneys and Bones

A clinical study published in the journal Clinical Endocrinology has warned that excessive intake of vitamin D supplements at high doses (more than 4,000 international units daily) over prolonged periods (exceeding six months) may lead to vitamin D toxicity (hypervitaminosis D), which causes dangerous calcium accumulation in the blood, threatening kidney, bone, and blood vessel functions.

Researchers explained that the initial symptoms are typically nausea, fatigue, and loss of appetite, while late-stage complications include kidney failure, soft tissue calcification, cardiac arrhythmias, and even bone damage due to impaired calcium and phosphorus metabolism.

The study highlighted two groups at particular risk:

• Individuals taking vitamin D supplements without medical supervision or without a genuine need (when baseline 25(OH)D levels are already normal, above 50 nanomoles per liter).

• Elderly individuals who may take high doses alongside other medications, such as thiazide diuretics or heart medications.

Dr. Vijay Kumar, an endocrinology consultant, emphasized that “many people believe vitamin D is safe at unlimited doses because it is fat-soluble, but in reality, its toxicity accumulates slowly and manifests after several months.”

He added that periodic monitoring of blood vitamin levels is essential for anyone taking therapeutic doses (more than 2,000 international units daily) for longer than three months.

It is worth noting that the U.S. Food and Drug Administration (FDA) sets the tolerable upper intake level at 4,000 international units daily for adults, although doses up to 10,000 international units may be prescribed for short periods in cases of severe deficiency under medical supervision.