New findings on diabetes, IBD, and Alzheimer’s

• We’ve rounded up the latest research from this past month on the health benefits of vitamin D supplements.
• Among the studies we’ve covered as of late is one on a genetic link between vitamin D supplementation and reduced risk of type 2 diabetes.
• Another study examines the link between higher vitamin D levels and biomarkers of Alzheimer’s disease.
• And lastly, a study examines the effects of vitamin D on the immune system in the context of inflammatory bowel disease (IBD).

Vitamin D, also known as the sunshine vitamin, is often touted as a cure-all, but does its hype live up to the evidence?

However, very high doses of vitamin D have also been linked to health risks such as nausea, vomiting, and weakness, which underscores the importance of seeking medical supervision before taking such supplements.

Medical News Today has compiled three of the latest pieces of research investigating the benefits of Vitamin D and summarized their key findings.

Published in the journal JAMA Network Open in April 2026, this study highlighted how vitamin D supplements can affect health outcomes depending on an individual’s genetics.

The researchers found that high dose vitamin D supplementation reduced the risk of type 2 diabetes for some people, but had no significant effect for others.

Particularly, people with the AC or CC variants of the vitamin D receptor gene had a 19% decrease in their risk of prediabetes developing into type 2 diabetes when taking 4,000 IU/day.

However, the researchers and medical experts Medical News Today spoke to underscored the dangers of taking too much vitamin D, while reiterating that these findings would need to be replicated in larger trials.

Diabetes is also a complex condition, where nutrition, genetics, exercise, weight, sleep, and many factors play a role in its development and progression, so a supplement alone is likely to do little in terms of prevention.

This study adds to growing evidence that healthcare is evolving toward individualized solutions and precision medicine.

Though genetic testing is not a widespread practice and remains costly, the study makes a case for identifying patients who will benefit the most from a preventive solution or treatment

“It’s promising, and my reaction is cautious optimism. The study suggests that vitamin D administration, in high risk individuals with certain genetic types, may be beneficial in preventing diabetes. It shows that in the future, we may be doing genetic testing to help determine if certain therapies can be used,” Jennifer Cheng, DO, chief of endocrinology at Hackensack Meridian Jersey Shore University Medical Center in New Jersey, who wasn’t involved in the study, told MNT.

Published in Neurology Open Access, an official journal of the American Academy of Neurology, in April 2026, this study found that higher vitamin D levels were associated with lower tau protein levels, a key biomarker for Alzheimer’s disease, years later.

Researchers from the University of Galway found that people with higher vitamin D levels in early middle age had lower tau protein levels on brain scans conducted an average of 16 years later.

However, they found no such link between beta-amyloid, another major biomarker for Alzheimer’s, and vitamin D levels in the blood.

This study serves as a reminder that modifiable risk factors are crucial in prevention or slowing down disease progression in Alzheimer’s and related dementias. If vitamin D deficiency can be addressed and treated earlier, the researchers hypothesize that this could reduce future dementia risk.

However, the study sample was small and homogeneous, participants had their vitamin D levels checked only once at the beginning of the study, and many other factors, such as lifestyle, may have affected the outcomes.

Steve Allder, MD, a consultant neurologist at Re:Cognition Health in London, the United Kingdom, who was not involved with the study, explained to MNT:

“Higher vitamin D levels may simply be a marker of overall better health rather than the driver of reduced tau pathology. For example, individuals with higher vitamin D are often more physically active, spend more time outdoors, and may have healthier diets, all of which are independently linked to better brain health.”

Published in the journal Cell Reports Medicine, this study suggested vitamin D supplements may benefit those with inflammatory bowel disease (IBD) by helping ‘reset’ the gut’s immune system.

Researchers monitored 48 adults with Crohn’s disease or ulcerative colitis, both of which fall under the umbrella of IBD, for 12 weeks and found that vitamin D helped reduce gut inflammation while promoting a more balanced immune response.

Vitamin D increased levels of the antibodies IgA and decreased levels of IgG, which helped the body recognize good gut bacteria while simultaneously preventing it from launching unnecessary attacks, as is what happens with an overactive immune system.

Although exploratory due to its scale and scope, this study could help change how we approach the treatment of inflammatory bowel disease (IBD), adding to the evidence that vitamin D could be an adjunct therapy.

In contrast to traditional treatments, which are based on suppressing the immune system, this study promotes “immune tolerance,” retraining the gut and immune system to coexist peacefully with gut bacteria.

John Mark Gubatan, MD, study author, and gastroenterologist at Mayo Clinic in Jacksonville, Florida, explained to MNT:

“Our exploratory study highlights [that] there could be potential benefits with vitamin D in controlling the interactions between the immune system and gut microbiome in patients with IBD and that further work is needed to understand the exact vitamin D levels and vitamin D supplementation strategies to support this in patients with IBD and other chronic inflammatory diseases.”