While vitamin D is known for its numerous health benefits , its supplementation is subject to many warnings. Between its genuine necessity and the risk of overdose, the question arises: is it safe to take? A recent study offers reassurance, suggesting that there is no risk, even with high doses, as long as they remain within certain limits.An essential nutrient, but often deficient
Vitamin D plays a fundamental role in the absorption of calcium and phosphate, essential for bone and muscle health . A deficiency in this vitamin is associated with numerous conditions: osteoporosis, sarcopenia, cognitive impairment, cardiovascular disease, and a weakened immune system.Vitamins and supplements
Lack of sun exposure , particularly in autumn and winter, explains why a large part of the population has insufficient levels of vitamin D. To remedy this, many choose to take supplements, sometimes throughout the year.However, this self-supplementation raises concerns. Some specialists favor ultra-high-dose medications (50,000 to 100,000 IU ampoules) available by prescription. Yet, research indicates that more moderate, but regular, intake may be more effective in preventing falls and fractures.
The potential dangers of excess vitamin D
Unlike water-soluble vitamins such as vitamin C, vitamin D is fat-soluble, meaning it accumulates
in the body instead of being quickly eliminated. An excess can lead to hypervitaminosis D, or even toxicity, although these cases are rare.The main risk is related to increased levels of calcium and phosphate in the blood. Since vitamin D promotes their absorption, an overdose can cause kidney overload and excessive accumulation of these minerals in the blood vessels. This calcification leads to stiffening of the arteries, thus increasing the risk of atherosclerosis and cardiovascular disease.Health
It is precisely to assess these risks that German researchers conducted a large-scale study on the effects of high levels of vitamin D in the blood.
A reassuring study on the effects of high supplementation
Several studies have shown a correlation between high blood levels of vitamin D (above the recommended 50 nmol/L) and an increase in blood calcium. A recent German study, conducted on over 445,000 individuals using the UK Biobank database, confirms this correlation. However, it found no negative effects on the kidneys or the cardiovascular system, even in participants with blood vitamin D levels reaching 100 nmol/L.For comparison, a 2017 study analyzed the effects of a level of 300 nmol/L, corresponding to a daily
intake of 15,000 IU. It concluded that these levels, although very rare, did not present any significant danger.
True cases of vitamin D toxicity are exceptional and generally occur at blood concentrations above 375 nmol/L. This threshold corresponds to a daily intake of approximately 50,000 IU for several months. When this toxicity is reached, it can cause severe hypercalcemia, leading to nausea, vomiting, weight loss, polyuria (increased urine production), and kidney failure.
What is the safe dose?The researchers behind the study believe that supplementation between 400 and 4,000 IU per day is safe for the majority of the population. Risks would only arise in cases of prolonged, massive intake, as illustrated by an extreme case in the United Kingdom, where a man reportedly consumed up to 150,000 IU daily , in combination with other supplements.
In France, the Esteban study conducted in 2015 revealed that a third of the adult population had a vitamin D deficiency, with levels below 50 nmol/L . However, a vitamin D deficiency is associated with an increased risk of cancer, cardiovascular disease, diabetes, autoimmune diseases, and depression .
Therefore, while supplementation is often beneficial, it should ideally be tailored to each
individual’s specific needs. A preliminary blood test would allow for adjusting intake and avoiding any risk of unnecessary excess.
