Vitamin D: high levels do no harm

Over the last years there has been a sharp rise in the use of vitamin D supplements. But toxic levels remain rare. According to a study published in "Mayo Clinic Proceedings, even vitamin D levels classified as high were found to do no harm.

For their analysis, researchers from the Mayo Clinic in Rochester (Minnesota) used data from the Rochester Epidemiology Project from the years 2002 until 2011. Out of 20,308 blood samples analysed, only eight per cent had vitamin D levels above 50 ng/mL - which was considered as "high"; not even one per cent had levels above 100 ng/mL.

"We found that even in those with high levels of vitamin D over 60 ng/ML, there was not an increased risk of hypercalcaemia, or elevated serum calcium, with increasing levels of vitamin D, said co-author Thomas D. Thacher.

Elevated vitamin D levels were mainly found in women older than 65. This was not surprising because this age group takes these supplements particularly often, said Thacher. In general, however, the rate of people with high levels has increased significantly over the last years: while the number was at nine out of 100,000 people in 2002, it increased to 233 out of 100,000 in 2011.

A true toxic vitamin D overdose was only found in one person - the vitamin D level had reached 364 ng/mL after taking 50,000 IU (international units) of vitamin D every day for three months The recommended upper limit for people with vitamin D deficiency is 4,000 IU a day.