Do you need vitamin D supplements? New study casts doubt on benefits

A new study casts doubt on the widespread use of high-dose vitamin D supplements, suggesting that the pills do not actually prevent bone fractures in healthy adults without vitamin D deficiencies.

The debate about the effectiveness of vitamin pills and supplements for the general population is not new. Despite the $150 billion-dollar industry's best efforts, research continues to show that the vitamin pills many of us think are doing our bodies good aren't actually doing much to make us healthier, TODAY previously reported.

“Vitamin D is really important for bone health, and (together) with calcium, it's incredibly important in terms of preventing osteoporosis,” NBC News medical contributor Dr. Natalie Azar said on TODAY Thursday. However, people without a vitamin D deficiency may not get added bone health benefits from high-dose daily supplement pills, according to a new study led by scientists at Harvard Medical School.

In the large randomized controlled trial, researchers tested whether 2000 IU (international units) per day of vitamin D3 supplements by itself would result in a lower risk of bone fractures compared to a placebo.

The study included over 25,800 participants, all over the age of 50, who were generally healthy. Participants were not selected for vitamin D deficiency, low bone mass, or osteoporosis, the authors wrote.

After following these participants for over five years, researchers found that vitamin D3 supplements "did not result in a significantly lower risk of fractures than (the) placebo among generally healthy midlife and older adults," the study authors wrote.

“This was a study done in people who weren’t selected for vitamin D deficiency, so it’s not unusual that you wouldn’t find an effect of vitamin D supplements,” said Azar.

Most people in the U.S. have adequate blood levels of vitamin D, but nearly one out of four people have levels that are inadequate or too low for bone and overall health, according to the NIH.

Vitamin D not only keeps bones strong and healthy — it’s also important for immune function, muscle function and brain health, Azar said. We get vitamin D from four main sources, she added.

1. Sunlight: Vitamin D is produced in the body when ultraviolet rays from sunlight strike the skin, which triggers vitamin D synthesis, according to the National Institutes of Health's Office of Dietary Supplements.
2. Foods: Vitamin D-rich foods include salmon, tuna, mackerel, fish oil and cod liver oil, said Azar.
3. Vitamin D-fortified foods: Fortified foods provide most of the vitamin D in American diets, according to NIH. These include milk, orange juice and fortified cereals, Azar said.
4. Dietary supplements: Pills either contain vitamin D2 (plant-derived) or D3 (often derived from animals but can be from lichen), according to NIH.

"The NIH does recommend that folks do take vitamin D or at least ingest vitamin D every day," said Azar.

If someone does not get enough vitamin D from their diet or sunlight, or has a medical condition that affects vitamin D levels or bone density, they will need to take supplements. That's because not getting enough vitamin D can cause muscle weakness, bone pain, and lead to osteoporosis, which causes bones to become fragile and break more easily, according to the NIH.

Risk factors for a vitamin D deficiency include gastric bypass surgery, liver or kidney disease, malabsorption, Crohn’s disease, obesity, having darker skin and not getting enough sun exposure, said Azar.

“If you have risk factors for vitamin D deficiency or osteoporosis, you definitely should be continuing your vitamin D and calcium,” said Azar.

For everyone else, more vitamin D isn’t necessarily better. So how much vitamin D do healthy people need? "The dose that was used in this study (2000s IU daily) is a little bit higher than what is normally recommended for most Americans," Azar said.

These are the recommended dietary allowances for vitamin D, according to the NIH:

0–12 months: 10 mcg (400 IU)

1–13 years: 15 mcg (600 IU)

14–18 years: 15 mcg (600 IU) 

19–50 years: 15 mcg (600 IU)

51–70 years: 15 mcg (600 IU) 

> 70 years: 20 mcg (800 IU)

"It’s really important also to point out again (that) this study was done in normal healthy people," said Azar. So the takeaway from this study "doesn't necessarily apply to people who have risks for osteoporosis or who have low bone mass," she added.

So if you have a vitamin D deficiency, you can and should absolutely keep taking your vitamin D, said Azar. But healthy individuals may not reap as much benefit from these supplements.