Studies surrounding vitamin D can be conflicting, often leading to confusion on the part of our patients. So our concierge primary care doctors in Jupiter thought we’d take a look at some of the newest findings about this essential vitamin.

Dueling Conclusions

As an example of how different researchers can draw opposite conclusions even from the same study, one doctor recently wrote in The Washington Post that a study she led “found no statistically significant reduction in cardiovascular disease or cancer” in a nationwide randomized trial of 26,000 adults over five years.

Furthermore, she wrote, “My colleagues and I have conducted further studies from VITAL [the study’s title] showing that vitamin D supplements do not decrease the risk of cognitive decline, depression, macular degeneration, atrial fibrillation or several other health conditions. The most recent report showed no reduction in the rate of bone fractures—once the vitamin’s most commonly touted benefit.”

She concluded that the vast majority of Americans are already getting all the vitamin D they need from brief sun exposure and a normal diet.

“Is it necessary for you to spend money on the supplement? For most healthy adults, the answer is no,” JoAnn Manson wrote in The Post.

However, this same researcher told the Harvard Gazette in January of this year that the VITAL study showed subjects who took vitamin D, or vitamin D and omega-3 fatty acids, had a significantly lower rate of autoimmune diseases such as rheumatoid arthritis and psoriasis than those who took a placebo.

“Given the benefits of vitamin D and omega-3s for reducing inflammation, we were particularly in whether they could protect against autoimmune diseases,” she said.

More Confusion

So maybe the vitamin has some value after all, at least for some.

Yet in 2018, another study published in the National Institutes of Health’s (NIH) National Library of Medicine looked at the prevalence of vitamin D deficiency in the U.S. population. In the introduction, the study’s authors wrote that, “Since foods containing natural vitamin D are rare, the primary source of the compound remains . . . exposure to ultraviolet rays in sunlight.”

It went on to assert that “subclinical vitamin D deficiency . . . plays a role in downstream clinical consequences, including cardiovascular disease, cancer, diabetes, osteoporosis, and fractures.”

Why the frequent discrepancy among various studies? One 2020 clinical study published in the journal BMJ sought to answer that question. 

“Our analysis of pooled raw data from each of the 10,933 trial participants allowed us to address the question of why vitamin D ‘worked’ in some trials, but not in others,” Adrian Martineau, a professor at Queen Mary University of London (QMUL) and a lead researcher on the study, wrote in a release.

Those who have the lowest levels of vitamin D in their blood seem to show the largest benefit, he said, along with those who took it daily or weekly, as opposed to intermittently.

The Last Word?

A fact sheet on vitamin D produced by the NIH’s Office of Dietary Supplements (ODS) updated last month summarized numerous studies, including the VITAL study.

For each of the most common health claims connected to vitamin D it reached the following conclusions:

Bone health – All adults should consume recommended amounts of vitamin D and calcium from foods and supplements.

Cancer – Taken together, studies to date do not indicate that vitamin D with or without calcium supplementation reduces the incidence of cancer, but adequate or higher levels might reduce cancer mortality rates.

Cardiovascular disease (CVD) – Overall, clinical trials show that vitamin D supplementation does not reduce CVD risk, even for people with low levels as measured in their blood.

Depression – Overall, clinical trials did not find that vitamin D supplements helped prevent or treat depressive symptoms or mild depression, especially in middle-aged to older adults who were not taking antidepressants.

Type 2 diabetes – Clinical trials provide little support for the benefits of vitamin D supplementation for glucose homeostasis.

Weight loss – Overall, the available research suggests that consuming higher amounts of vitamin D or taking vitamin D supplements does not promote weight loss.

And although the COVID-19 pandemic sparked hope that vitamin D could help prevent or reduce the severity of the illness, two new clinical studies released this month found that it didn’t help with the coronavirus or any other type of respiratory virus.

Vitamin D Overdose?

According to the NIH, the recommended daily allowances for vitamin D are:

• 0-12 months: 10 mcg (400 IU)
• 1-70 years: 15 mcg (600 IU)
• >70 years: 20 mcg (800 IU)

And while many people who supplement with vitamin D take much higher doses than that, too much can be dangerous. Vitamin D is a fat-soluble vitamin, which means it tends to be stored in the body’s fat and can lead to accidental overdoses. 

The upper limit of safety appears to be 100 mcg (4,000 IU) daily.

Those who take more than that could experience side effects from supplementing with vitamin D, including nausea and vomiting, constipation, weakness, and kidney damage, among others.

Overall, most studies seem to show that supplementing with vitamin D doesn’t have much effect on various conditions. On the other hand, moderate doses from a reputable manufacturer are generally considered safe. So if you think you could benefit from vitamin D supplements, the decision is up to you.