5 New Things Scientists Have Learned About Vitamin D In 2026

Hearing loss is already associated with a greater risk of depression. But a large study1 suggests vitamin D status may also play a role. Researchers followed more than 96,000 adults with hearing impairment and found that those with vitamin D deficiency (blood levels below 20 ng/mL) had a 57% higher risk of developing depression over the next 12 years than those with sufficient vitamin D levels.

Vitamin D deficiency was also associated with a higher risk of recurrent depression and all-cause mortality. While researchers say vitamin D status could serve as a useful risk marker in this population, future clinical trials will be needed to determine whether correcting a deficiency changes those outcomes.

Vitamin D is important for brain health (even long before signs of cognitive decline appear). In a study of nearly 800 dementia-free adults, researchers measured participants’ vitamin D levels during early midlife and then used brain PET scans about 16 years later to assess markers associated with Alzheimer’s disease.

Higher vitamin D levels in midlife were associated with lower levels of tau buildup, a protein involved in Alzheimer’s disease progression, but were not linked to amyloid plaque burden. The findings suggest that maintaining adequate vitamin D status earlier in life may be one factor associated with healthier brain aging, though more research is needed to understand how vitamin D may influence dementia-related changes over time.

Low vitamin D levels may lead your stomach wide open to infection. Helicobacter pylori (H. pylori) is a bacterial infection that impacts the stomach lining (and about 40-50% of the global population2). Most people don’t know they have this infection, which you can get via personal contact or contaminated food and water. 

A new study found that vitamin D deficiency was far more common in those who tested positive for H. Pylori. Vitamin D helps maintain the integrity of the mucosal lining and supports the immune surveillance that keeps harmful bacteria from taking hold.

In a study of more than 500 women with invasive breast cancer1, researchers tracked vitamin D levels at three points throughout treatment instead of relying on a single blood test. Nearly two-thirds of participants started out with severe vitamin D deficiency.

Women whose vitamin D levels remained low (or declined over time) had significantly worse event-free survival than those who maintained healthy vitamin D levels. While this study doesn’t prove that improving vitamin D status leads to better outcomes, it indicates that regularly monitoring vitamin D throughout treatment (not just once at diagnosis) could provide valuable insight into a patient's prognosis.

Yes, vitamin D may impact how tall people grow, according to new genetic research. Using a Mendelian randomization approach (a method that uses genetic data to explore potential causal relationships) researchers found that higher vitamin D levels were associated with slightly greater height among adults of European ancestry.

For example, for every meaningful increase in vitamin D levels, height increased by roughly 0.2 to nearly 1 centimeter. While that may sound modest, small differences can add up over time. 

The findings support the idea that adequate vitamin D during growth and development may help people reach their genetic height potential, likely through its well-established role in bone formation and mineral metabolism.

About 29% of U.S. adults3 are deficient in vitamin D (have blood levels less than 20 ng/mL), and 41%31 have insufficient vitamin D levels (less than 30 ng/mL). So many of us could use a boost in this nutrient.

However, it’s hard get enough of through diet alone (although fatty fish, egg yolks, and fortified foods provide some of this vitamin). Also, relying on sun exposure (even in a safe way) isn't enough to raise low vitamin D levels or maintain optimal ones.

That's why vitamin D supplementation is so crucial. This is a great option for raising stubbornly low vitamin D levels. For more recommendations, check out this expert-vetted list of RD-approved vitamin D supplements.