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A recent study has found more evidence to support a causal relationship between vitamin D deficiency and an increased risk of death. Morsa Images/Getty Images
  • Vitamin D is a fat-soluble nutrient the body needs for maintaining bone health and immune system function.
  • Previous studies suggest that vitamin D may also help reduce inflammation and the risk of certain health conditions. Some research has also linked low vitamin D levels to increased mortality risk.
  • Recent research from the University of South Australia has found evidence to support a causal relationship between vitamin D deficiency and premature death.
  • The study authors say these findings underscore the need to develop effective strategies to prevent vitamin D deficiencies across the population.

Also known as the “sunshine vitamin,” vitamin D is a fat-soluble vitamin the body produces from sun exposure. It’s also present in certain common foods.

Vitamin D has several functions in the body. For example, it helps regulate calcium and phosphorus for bone health, reduces inflammation, and supports the immune system.

What’s more, vitamin D may have other health benefits, including reducing the risk of certain health conditions like cardiovascular disease (CVD) and multiple sclerosis (MS).

But not getting enough vitamin D through sun absorption or dietary intake can lead to vitamin D deficiency, which can negatively impact health.

For example, a 2017 meta-analysis found an association between low vitamin D levels and increased risk of all-cause mortality. Moreover, in a 2021 study, researchers found genetic evidence that suggests a causal relationship between low vitamin D levels and mortality.

Recently, a new genetic study from the University of South Australia published in the Annals of Internal Medicine found more evidence to support a causal relationship between vitamin D deficiency and increased mortality.

Specifically, the researchers estimate that the odds of all-cause mortality increase by 25% for individuals with vitamin D serum levels of 25 nmol/L compared to people with serum concentrations of 50 nmol/L.

“We found evidence for excess mortality in individuals who are vitamin D deficient and that by increasing vitamin D levels in these individuals, we can reduce mortality risk,” study author Elina Hypponen, PhD, a University of South Australia professor and director of the Australian Centre for Precision Health, told Healthline.

Although still widely debated, experts generally define vitamin D deficiency as serum 25(OH)D levels below 30 nmol/L. Vitamin D concentrations between 30–49 nmol/L are considered insufficient.

Still, other evidence suggests that vitamin D deficiency is defined as serum 25(OH)D concentrations of less than 50 nmol/L — and severe vitamin D deficiency occurs when serum concentrations fall below 30 nmol/L.

The study authors note that recent estimates indicate up to 50% of the population may be vitamin D deficient — depending on geographical location and population demographics.

The research team recruited 307,601 participants from the U.K. Biobank to examine associations between vitamin D and mortality risk. The participants were between the ages of 37–73 years at the time of recruitment, and all were of white European ancestry.

Then, they obtained the participant’s genetic data and measurements of serum 25-hydroxyvitamin D 25(OH)D.

Over a 14-year follow-up, the scientists also recorded all-cause mortality and deaths caused by specific diseases, including:

  • cardiovascular disease
  • cancer
  • respiratory disease

When the research concluded, the scientists recorded 18,700 deaths among the participants.

Using nonlinear Mendelian randomization analysis, the researchers discovered that the risk of death decreased significantly with increasing vitamin D levels — but that association plateaued when serum levels reached 50 nmol/L.

The scientists also found that genetically predicted 25(OH)D concentrations below 25 nmol/L had the strongest association with increased mortality risk.

Moreover, the researchers observed the same association when they analyzed deaths from cancer, cardiovascular disease, and respiratory disease.

“In this study, we found evidence for a benefit across all the main causes of death, including cardiovascular disease, cancer, and respiratory disease-related mortality,” Hypponen said.

“However, in most cases, any benefit for increasing vitamin D levels was restricted to those individuals who have very low concentrations.”

Additionally, Hypponen said the study was the first to show a reduction in mortality related to respiratory diseases.

“[It’s] safe to say this is the most comprehensive study to provide evidence for the role of vitamin D in the prevention of premature mortality,” she added.

According to the study authors, participants who were nonsmokers, physically active, and living in southern areas had higher concentrations of vitamin D. People with lower body mass index and less socioeconomic challenges also had higher levels.

Previous genetic research by Hypponen and her colleague Ang Zhou, PhD, found an association between low vitamin D status and higher C-reactive protein — an inflammatory biomarker in the blood.

“It is possible that lower inflammation may in part help explain these findings; however, there are also many other mechanisms,” Hypponen said.

“It is important to remember that vitamin D is a pro-hormone, which has receptors throughout the body, including most major organs. If we allow the levels of this hormone to go very low, it is possible that multiple systems get disrupted, leading to [an] increase in overall frailty, and as our results suggest, an increase in premature mortality.”

Although the study used a large number of participants, all were individuals of white European ancestry.

So, whether these results translate to individuals of other racial or ethnic groups is unknown.

However, the researchers also included sensitivity analyses on non-white ethnic groups in the analysis.

Because of this, the scientists suggest the study results could be similar outside of white ethnic populations.

Dr. Janice Johnston, chief medical officer and co-founder of Redirect Health, told Healthline that healthcare professionals don’t always order routine checks for vitamin D levels, which may be attributed to a lack of coverage by insurance companies for general screening.

“If you have certain [health] conditions or risk factors for vitamin D deficiency, you should ask your doctor or healthcare [professional] to order a test,” she said.

“For adults who have already been found vitamin D deficient, a blood test may be recommended to monitor blood levels 3 months after beginning treatment.”

Determining how much vitamin D an individual requires is challenging, as it depends on factors such as sun exposure and time of year.

According to the National Institutes of Health (NIH), the average recommended amount of vitamin D for healthy adults is 600 International Units (IU) per day. Adults 71 years and older should try to get 800 IU per day.

Moreover, the 2011 Endocrine Society Clinical Practice Guidelines suggest that treatment for vitamin D deficient adults is 50,000 IU of vitamin D2 or vitamin D3 once a week for eight weeks or 6000 IU of vitamin D2 or vitamin D3 daily.

Then, once 25(OH)D levels are adequate, the recommended maintenance dose is 1500–2000 IU per day.

But too much vitamin D could also be detrimental to health.

“I would be cautious of using high dose or ‘bolus’ approaches given they have in many cases shown to be less effective than regular modest dose vitamin D supplementation with respect to achieving the desired health benefit and not just the higher vitamin D levels,” Hypponen said.

Johnston suggested that eating more foods containing vitamin D and getting more sunlight can help increase vitamin D levels if you’re deficient.

Recommended food sources of vitamin D include:

  • salmon
  • egg yolks
  • dairy products fortified with vitamin D

“Additionally, getting in daily walks outside in the sun will be helpful in treating vitamin D deficiencies too — but don’t forget to wear sunscreen,” Johnston said.

“If you’re found vitamin D deficient, your healthcare [professional may] recommend taking vitamin D supplements.”

Vitamin D has many vital functions in the body, and studies suggest that people with vitamin D deficiency may be at a higher risk of certain health conditions.

Some research has also found associations between low vitamin D levels and mortality.

The new study’s results provide more evidence to support that maintaining adequate vitamin D levels may be critical for preventing premature death from all causes.

“In my opinion, the most important thing is that we find an effective strategy that will ensure all have at least minimal reserves of vitamin D,” Hypponen said.

“At the population level, prevention is the key. In clinical settings, monitoring and treating vitamin D deficiency can also help.”