Medically reviewed by Anna Goldman, MD.

New research has found that large doses of vitamin D could prolong the “honeymoon phase” in children and young adults newly diagnosed with type 1 diabetes (T1D). 

Published on March 5, 2024, by JAMA Network Open, the study suggests that this relatively affordable intervention could delay the need for daily insulin therapy.

“Type 1 diabetes affects millions of people and treatment options can often be costly,” said Benjamin Nwosu, MD, chief of endocrinology at Northwell Health and principal author of the paper. His study shines a light on the potential benefits of vitamin D.

What is the Honeymoon Phase?

The honeymoon phase describes the sometimes dramatic increase in a person’s natural insulin production immediately after their diagnosis of type 1 diabetes, after starting daily insulin therapy.

While type 1 diabetes eventually destroys all or nearly all of the beta cells — the cells responsible for making insulin — this doesn’t happen immediately. Nwosu said that people newly diagnosed with T1D still retain approximately 30 to 50 percent of beta cell function. Protecting and prolonging that beta cell function is the aim of many clinical trials and investigative therapies.

Vitamin D and T1D

While it isn’t discussed much in patient care, research has focused on vitamin D levels in T1D for many years.

Past research has suggested that healthy vitamin D levels can improve many aspects of diabetes management and progression:

There is an association between vitamin D deficiency and the risk of developing T1D 
Many people have low vitamin D levels at the time of T1D diagnosis
Vitamin D plays a critical role in your immune system and beta-cell function
Low vitamin D levels may contribute to insulin resistance
Vitamin D supplementation has improved insulin sensitivity by 60% 
Vitamin D supplementation has been shown to improve insulin sensitivity and A1C levels

Despite this abundance of research, health authorities have never formally concluded that higher doses of vitamin D should be recommended to people with T1D.

“There is a ‘vitamin D hypothesis’,” Nwosu explained to Diabetes Daily. “It suggests that the further you move away from the equator, the higher the prevalence of autoimmune diseases like type 1 diabetes and rheumatoid arthritis are. When you’re getting enough vitamin D from the sun, it protects you from some of those autoimmune triggers. We know vitamin D is an immunomodulator, anti-inflammatory, and helps the body produce functional insulin.”

Routine sun exposure for most people around the world is not enough to raise vitamin D levels to optimal levels. If you’re not living in a tropical climate, or if you spend relatively little time outdoors, getting more vitamin D through a supplement may be advisable. Nwosu added that supplementing with vitamin D2 or vitamin D3 is equally effective.

The Study: 50,000 IUs per Week

The study enrolled 48 participants between the ages of 10 and 21, all of whom had recently been diagnosed with type 1 diabetes. Researchers followed their progress for an entire year.

The treated group took a weekly dose of 50,000 IUs of vitamin D ergocalciferol (vitamin D2) orally for two months, then biweekly for 10 months. This amount was within the range of typical recommendations for vitamin D supplementation. A Cleveland Clinic review (PDF) suggested that people with demonstrated vitamin D deficiency could take as much as 5,000 IUs per day, and that maintenance doses should start at 2,000 IUs per day.

Another group took a placebo.

Participants underwent glucose tolerance tests before and after the 12 months to compare three factors:

C-peptide: an amino acid that indicates insulin production levels
Fasting glucose levels: your blood glucose level in the morning before eating
Proinsulin: a substance produced by the pancreas that is converted to insulin

The results revealed that participants receiving vitamin D saw an improved ratio of proinsulin to C-peptide, suggesting increased insulin production. It also delayed the loss of C-peptide, concluding that vitamin D protected the insulin-producing beta cells.

Nwosu conducted past research on the safety of taking high doses of vitamin D, all with a clear conclusion: Vitamin D toxicity isn’t as likely as we’ve been told.

“Our research in 2021 and 2022 showed that even with these high doses of vitamin D, participants’ peak levels didn’t even pass 40 ng/mL,” explained Nwosu, adding that ideal ranges are between 30 to 60 ng/mL. “We monitored participants’ vitamin D levels very closely, but the body has a way of taking what it needs and converting the rest into inert products.”

Should You Take Vitamin D if You Have T1D?

Nwosu’s evidence suggests that people with newly diagnosed T1D should consider taking a vitamin D supplement. We asked the researcher if he’d go even further: Should everyone with type 1 diabetes be taking vitamin D?

“Yes,” said Nwosu. “Any child or adult newly diagnosed or with longstanding type 1 diabetes can supplement with vitamin D. If you get your levels tested and your vitamin D is below 30 ng/mL, you should start supplementing. If you’re above 30 ng/mL, you probably don’t need to.” 

Even in those with longstanding T1D, Nwosu said, vitamin D supplementation could probably still improve glucose metabolism and inflammation. 

It’s important to note that vitamin D supplementation has not been broadly adopted or emphasized by the diabetes medical field. Nwosu maintains that other past studies that found minimal benefits for vitamin D supplementation were not as rigorous as his research. 

“All studies are not the same. We used standardized insulin protocols while most studies don’t track proinsulin at all. This was also a randomized control study, which most studies are not. There are many reasons a study’s results can be negative — you have to do it very well to get reliable results.”

Nwosu hopes vitamin D supplementation also gains more consideration as a treatment for preventing or delaying T1D.

“It is exciting to know that vitamin D could protect the beta cells of the pancreas and increase the natural production of good and functional insulin in these patients. I see vitamin D as a very special molecule that can do so much more than we’ve even been able to study yet,” said Nwosu. “If vitamin D can protect your beta cells after you’ve been diagnosed, it should be able to help before the time of diagnosis, too.”

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