A study in Nature communications in 2025 looked at more than 22,000 older adults in the United States in a randomised clinical trial with vitamin D3. After just over five years, vitamin D did not clearly reduce new cases of type 2 diabetes in this general population, although a pooled review of four trials suggested a small reduction in risk, particularly in people without obesity.
For those concerned about their metabolic and cardiovascular health, the message is nuanced. Vitamin D is not an absolute barrier to diabetes, but it does appear to be involved in glucose balance and insulin function, especially when combined with other healthy habits and nutrients such as omega-3 fatty acids.
What the VITAL study did with vitamin D and what it found in type 2 diabetes
The analysis was integrated into the VITAL trial, a large, randomised, double-blind study of more than 22,000 adults aged about 67 years on average without diabetes at baseline. They compared 2000 international units daily of vitamin D3 against placebo for a median of 5.3 years and recorded how many people developed type 2 diabetes.
In the vitamin D group, slightly fewer than four cases of diabetes occurred per 1000 people per year, compared to slightly more than four in the placebo group. This difference translated into a relative reduction of 9 per cent, but the margin of statistical error included no effect, so it was considered a small change.
When the authors combined these data with three other similar trials in a meta-analysis, the picture was somewhat clearer. Overall, more than 25,000 participants showed an approximate 11 per cent reduction in diabetes risk with vitamin D, and this reduction was as high as 25 per cent in people without obesity. Still, these are modest effects that must be interpreted as part of an overall healthy lifestyle.
How vitamin D and omega-3s are involved in glucose metabolism
Vitamin D is best known for its role in bone and defence, but it is also expressed in the pancreas and in insulin-responsive tissues. Mechanistic studies suggest that it may promote the function of beta cells, which produce insulin, and improve tissue sensitivity to insulin.
In the subgroup of the VITAL study who came for face-to-face visits, markers such as fasting glucose and glycosylated haemoglobin, which reflect mid-term glucose control, were measured. No relevant changes in these parameters were observed after two years, indicating that the effect of vitamin D, if any, is modest and probably more visible in people with previous deficiencies or at high metabolic risk.
In parallel, the VITAL trial also included a long-chain omega-3 fatty acid arm, mainly EPA and DHA. These marine lipids are involved in cell membrane fluidity and the resolution of low-grade inflammation, a process closely linked to both insulin resistance and cardiovascular health. Although the analysis we discuss focuses on vitamin D, the combination of vitamin D and omega-3s points to a physiological strategy that acts on several axes at once, inflammation, metabolism and vascular function.
Daily habits that reinforce the effect of vitamin D and omega-3s
The authors of the study point out that type 2 diabetes is directly linked to excess weight, lack of physical activity and a diet rich in fast sugars and ultra-processed products. Therefore, supplements only make sense as a complement to a solid foundation of habits.
In practice, this means prioritising fresh foods, vegetables, whole fruits, legumes and whole grains, reducing sugary drinks and pastries, and choosing quality fats such as olive oil, nuts and oily fish rich in omega-3. Maintaining a stable weight and moving daily, for example with brisk walking or strength training, directly improves insulin sensitivity.
Vitamin D is further supported by moderate sun exposure, always with caution to protect the skin, and foods such as oily fish, eggs and fortified dairy products. Combining these pillars with adequate omega-3 intake creates a more stable metabolic and cardiovascular environment, which is precisely the physiological target on which some advanced supplement formulations are designed.
How Nutribiolite OMEGA 3 EPA 400 mg + DHA 300 mg fits with this evidence
Although the VITAL T2D analysis focused on vitamin D, it is part of a larger trial that evaluated vitamin D3 and long-chain omega-3 fatty acids together for the primary prevention of cardiovascular disease. This combination of nutrients matches the focus of Nutribiolite’s OMEGA 3 EPA 400 mg + DHA 300 mg supplement, which integrates concentrated marine omega-3s together with vitamin D3 and vitamin K2.
The fatty acids eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA, are involved in regulating inflammation and maintaining the function of cell membranes, including vascular tissues. At a physiological level, this relates to a more balanced circulation and a metabolic environment less prone to chronic low-grade inflammation, which often accompanies excess weight and impaired glucose control.
Vitamin D3 in the formula contributes to the maintenance of muscle and immune system function and is involved in pathways that have also been linked to insulin sensitivity. The VITAL study shows that daily doses of vitamin D3 in older adults have a modest effect on the onset of diabetes, but reinforces the idea that maintaining adequate levels is a reasonable part of an overall preventive strategy.
Vitamin K2, present in OMEGA 3 EPA 400 mg + DHA 300 mg, adds an additional axis, as it participates in the correct use of calcium and in the protection of the vascular structure. The combination of omega 3 with vitamins D3 and K2 thus seeks to support cardiovascular and bone health in a coordinated way, while accompanying metabolic processes that are also discussed in studies such as VITAL.
Omega 3 EPA and DHA supplement with vitamins D3 and K2, designed for adults who take care of their metabolism and cardiovascular health as part of a healthy lifestyle.
OMEGA 3 EPA 400 mg + DHA 300 mg is aimed at adults who already pay attention to their diet, physical activity and rest and want additional support in the form of key nutrients with scientific backing. It is not intended to replace lifestyle habits or medication, but to add another tool in building a solid physiological foundation for the heart, joints and metabolism.
Final message, what this study adds to your daily routine
The VITAL trial and its analysis of type 2 diabetes show that vitamin D, even at relatively high doses, does not by itself change the course of metabolism in older adults, although there is a slight reduction in risk when several studies are analysed together, especially in people without obesity.
The practical lesson is clear. Watching your weight, moving daily, prioritising fresh foods and ensuring a good intake of vitamin D and omega-3s lay the foundation for a more stable metabolism and cardiovascular system. Supplements such as OMEGA 3 EPA 400 mg + DHA 300 mg fit into this logic of physiological support, always within a broader strategy of self-care.
This content is informative and does not replace the advice of a health professional.
Frequently asked questions
What does it mean that vitamin D has a modest effect on type 2 diabetes?
It means that, in the trials reviewed, the reduction in diabetes risk was small and not sufficient to be considered a stand-alone tool. Vitamin D may support metabolism, but weight, diet and exercise remain the main pillars.
Why are vitamin D and omega-3 combined in some supplements?
Vitamin D is involved in metabolism, muscle function and immunity, while omega-3 EPA and DHA support cardiovascular health and modulate inflammation. Together they act on physiological pathways related to the heart and glucose control, which reinforces their interest in adults taking care of these aspects.
Does it make sense to take omega-3s if I already eat oily fish several times a week?
A diet of frequent oily fish already provides a base of EPA and DHA. Some people opt for a supplement when their fish intake is irregular or when they are looking for a more concentrated and consistent dose, always within a healthy lifestyle.
What role does vitamin K2 play in a formula with omega-3 and vitamin D3?
Vitamin K2 helps to direct calcium to the bones and prevent it from building up in the walls of blood vessels. In combination with vitamin D3 and omega-3, it contributes to a comprehensive approach to bone and cardiovascular health.
What type of person is OMEGA 3 EPA 400 mg + DHA 300 mg suitable for?
It is intended for adults who want to support their cardiovascular, joint and metabolic health with a combination of concentrated marine omega-3s and vitamins D3 and K2. It makes the most sense for people who already take care of their diet, move regularly and are looking for additional physiological support.
