Vitamin D-rich diet linked to lower blood sugar levels

A diet rich in vitamin D, featuring foods like eggs, oily fish and red meat, may be more effective at lowering blood sugar levels in people newly diagnosed with type 2 diabetes than taking vitamin D supplements or increasing sun exposure, results from a small clinical trial suggest.

Blood sugar control is critical for patients with type 2 diabetes to prevent long-term health problems such as heart disease, stroke, vision loss and nerve damage. Some newly diagnosed patients prefer to try lifestyle interventions before taking anti-diabetic prescription medicine to lower their blood sugar. 

Dietitian and lead author Dr Fay Yu said vitamin D deficiency has been linked to an increased risk of developing type 2 diabetes. However, the role of vitamin D in preventing and managing diabetes is debated, and previous studies have shown mixed results.

“Vitamin D levels can be boosted in three main ways: Exposure to sunlight, eating foods rich in vitamin D and taking vitamin D supplements,” said Dr Yu, who conducted the study as part of her PhD research at the University of Technology Sydney (UTS). 

“Our aim was to compare, for the first time, these three different methods of boosting vitamin D, and to measure the impact on blood sugar levels over nine months,” she said.

The results were recently published in the journal Diabetes, Obesity and Metabolism: The role of vitamin D in glycaemic control in patients with type 2 diabetes—A pilot D4D trial, with co-authors UTS Professor Hui Chen and Adjunct Professor Danforn Lim.

The clinical trial included 60 participants divided into four groups; sun exposure, diet, Vitamin D supplement, or waitlist, with HbA1c (a long-term measure of blood sugar levels), cholesterol and vitamin D levels tested at baseline, three months and nine months.

While most participants were not Vitamin D deficient at the beginning of the study, all groups except the waitlist group saw an increase in their vitamin D levels.

The study found significant reductions in HbA1c blood sugar levels in both the diet and supplement groups after three months, with the most significant changes observed in the diet group. 

“Specific dietary recommendations to increase Vitamin D included eating six to seven eggs per week, two to three servings of red meat, and two to three servings of oily fish such as sardines and salmon, as well as eight to ten servings of semi trimmed pork or chicken,” said Professor Hui Chen. 

“Foods rich in vitamin D generally have a low glycemic index (GI) and are high in protein, which can also positively affect long term blood sugar levels,” she said.

As a practicing Specialist GP researcher, Adjunct Professor Lim considered this study significant for GPs, endocrinologists and diabetic educators as it provides practical, evidence-based insights to support personalised care in type 2 diabetes management. 

“For the frontline health practitioners, it highlights the value of dietary advice as an empowering alternative for patients hesitant about medication or supplement intake. 

“This study emphasises the importance of integrating lifestyle medicine into glycaemic control strategies, offering a holistic approach that improves both blood sugar and overall health outcomes," said Adjunct Professor Lim. 

The researchers did not find a strong linear correlation between Vitamin D levels and HbA1c. The sun exposure group saw a significant increase in vitamin D levels, and improved blood cholesterol levels, but little change to blood sugar levels.

“Further research is needed to untangle the complex relationships between vitamin D, diet, sun exposure, and health outcomes,” said Dr Yu.