"Getting too much vitamin D can compromise its benefits and create health risks. From age to where you live, here are the factors."

A study of older adults at risk of falls found that those who took the highest levels of vitamin D were more likely to fall.

Low blood levels of vitamin D have been linked to an increased risk of a number of diseases, including heart disease, diabetes and cancer, mood disorders and dementia.It's no wonder, then, that vitamin D supplements are so popular.However, many people who take vitamin D supplements do not have signs of deficiency or an underlying condition that would benefit from them, and some take doses above the safe limit.

How much vitamin D do you need?

As Health Harvard reminds us, the current Recommended Daily Allowance (RDA) for vitamin D is 20 micrograms (mcg or mg) or 800 international units (IU) for people over 70 years of age and 15 micrograms (600 IU) for people between 1 and 70 years of age.

The Endocrine Society's 2024 guidelines state that healthy adults under the age of 75 should not take vitamin D supplements. The guidelines recommend supplements only for certain groups: children (1 to 18 years old), adults 75 years and older, pregnant women, and people at high risk for prediabetes.

health benefits

Nicknamed the “sunshine vitamin” because the body produces it after exposure to the sun, vitamin D has long been known to support bone health by increasing the absorption of calcium and phosphorus.Since the turn of the century, research into the role of vitamin D in various health conditions has grown rapidly.

Although there is strong evidence supporting the role of vitamin D in bone health, the evidence for its protection against other diseases is inconclusive. For example, the VITAL (Vitamin D and Omega-3 Study) study, which involved more than 25,000 participants age 50 and older across the United States, found that people who took vitamin D supplements did not have a reduced incidence of heart disease, stroke, orHowever, among people who later developed cancer, those who took vitamin D supplements for at least two years were 25 percent less likely to die from cancer than those who received a placebo.

Risk reduction

Other analyzes of data from the VITAL study found that five years of vitamin D supplementation was associated with a 22% reduced risk of developing autoimmune diseases such as rheumatoid arthritis or psoriasis, and four years of supplementation was associated with slower cellular aging.However, data from the VITAL study showed that vitamin D supplementation was not effective in preventing depression.

And as of 2025, two randomized, controlled clinical trials have found no effect of vitamin D supplementation on cognitive function, memory (the VitaMIND study), or dementia (the Finnish Vitamin D study).

Factors for vitamin D levels

- Where do you live?People living in northern regions (latitudes above 37°) are at risk of vitamin D deficiency because their skin is exposed to less sunlight during the winter months.

- Your age.The skin's ability to produce vitamin D decreases with age.If you're over 65, your skin produces only a quarter of the vitamin D it produced in your 20s.

- Skin color.People with dark skin typically have lower levels of vitamin D than people with fair skin.On average, African Americans have the same amount of vitamin D in their blood as white Americans.

- Your weight.If the body mass index is more than 30, there may be less vitamin D in the blood.Because vitamin D is stored in adipose tissue, people with excess body fat have less vitamin D in their blood where the body can use it.

- The food we eat.With the exception of some types of fish, few foods naturally contain high levels of vitamin D. Most cow's milk is fortified with vitamin D, a process that was introduced by the US government in the 1930s to fight rickets, a bone-weakening disease caused by a lack of vitamin D. Many plant-based beverages are also fortified, such as breakfast cereals and some types of orange juice.

- certain health conditions.People with inflammatory bowel disease, liver disease, or cystic fibrosis (among others) may have trouble absorbing vitamin D, which can lead to a deficiency.

High doses of vitamin D can be dangerous.Vitamin D is not water soluble, so it cannot be extracted from the skin;as a result, excess vitamin D accumulates in body tissues and blood.

Overdoses

In rare cases, taking too many vitamin D supplements can be toxic: it can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, causing deposits in the arteries or soft tissues.High doses of vitamin D can also cause kidney stones.

A study of older people who were already at risk of falling found an increased risk of falling in those who took the highest dose of vitamin D (50 mcg to 100 mcg, or 2,000 IU to 4,000 IU), compared to those who took the lowest dose (6.3 to 25 mcg, or 250 IU to 1,000 IU).A follow-up analysis also suggested that people with high blood levels of vitamin D after taking supplements may have a greater risk of falling compared to people with low levels.