Researchers studied 84 people with obesity who weren’t getting enough vitamin D. They compared three approaches: following a Mediterranean diet alone, adding one type of vitamin D supplement (cholecalciferol), or adding a different type (calcifediol). After three months, all groups lost weight, but the group taking calcifediol lost the most weight, had the biggest improvement in belly fat, and got their vitamin D levels back to normal faster. This suggests that calcifediol might be a better choice than regular vitamin D supplements for people with obesity who need to boost their vitamin D levels.

The Quick Take

  • What they studied: Whether two different forms of vitamin D supplements work differently when combined with a Mediterranean diet for helping people with obesity lose weight and reduce belly fat
  • Who participated: 84 adults with obesity who had low vitamin D levels. They were split into three groups: one group followed a Mediterranean diet only, one added regular vitamin D (cholecalciferol), and one added a different form of vitamin D (calcifediol)
  • Key finding: After 3 months, the group taking calcifediol lost the most weight (about 17 pounds), had the biggest improvement in belly fat measurements, and raised their vitamin D levels by 20 ng/mL—more than the other groups
  • What it means for you: If you have obesity and low vitamin D, calcifediol might help you lose more weight and reduce harmful belly fat better than regular vitamin D supplements. However, talk to your doctor before starting any supplement, as this is one study and more research is needed

The Research Details

This was a retrospective study, meaning researchers looked back at medical records of 84 people who had already received treatment. The participants were divided into three groups based on what treatment they actually received: some followed a Mediterranean diet alone, some added regular vitamin D supplements, and some added a different type of vitamin D called calcifediol. Everyone was measured at the start and again after 3 months to see how much weight they lost, how their vitamin D levels changed, and how much belly fat they had.

The Mediterranean diet used in this study was a lower-calorie version designed to help with weight loss. Researchers measured not just weight, but also body composition (how much is muscle versus fat) and specific belly fat measurements that doctors use to assess health risks. This approach gave them a more complete picture than just looking at the scale.

This study design is useful because it looks at real-world results from actual patients rather than a controlled lab setting. By comparing three different approaches at the same time, researchers could see which combination worked best. The focus on belly fat is important because belly fat is particularly harmful to health, even if overall weight is similar

This study has some strengths: it measured multiple important health markers, not just weight, and it looked at real patients in actual practice. However, because it’s retrospective (looking backward at records), researchers couldn’t control all the factors that might affect results. The sample size of 84 is moderate—larger studies would give more confidence in the findings. The study lasted only 3 months, so we don’t know if these benefits continue longer

What the Results Show

All three groups showed meaningful weight loss and improvements in body measurements after 3 months, which shows that the Mediterranean diet itself is helpful. However, the group taking calcifediol (the special form of vitamin D) did noticeably better than the other two groups.

The calcifediol group lost about 7.8 kilograms (17 pounds) compared to smaller losses in the other groups. More importantly, their vitamin D levels increased by 20 ng/mL, which is a significant jump that brought most participants into the healthy range. Their belly fat measurements improved more than the other groups, which is particularly important because belly fat is linked to serious health problems like heart disease and diabetes.

Another interesting finding was that only the calcifediol group actually increased their muscle mass while losing fat. This is ideal for weight loss because muscle helps your body burn calories. The other groups lost weight but didn’t gain muscle, suggesting they may have lost both fat and muscle.

The research showed that calcifediol’s benefits for reducing belly fat happened independently of overall weight loss—meaning it wasn’t just because people lost more weight. This suggests calcifediol has a special effect on belly fat specifically. The study also found that regular vitamin D (cholecalciferol) was less effective at raising vitamin D levels and reducing belly fat compared to calcifediol, even though both are vitamin D supplements

Previous research has shown that vitamin D deficiency and obesity often go together, and that vitamin D plays a role in how the body stores fat. This study builds on that knowledge by showing that not all vitamin D supplements work equally well. Calcifediol appears to be more effective than the standard form (cholecalciferol) that most people take, which is a new and important finding that could change how doctors treat vitamin D deficiency in obese patients

This study only lasted 3 months, so we don’t know if the benefits continue or fade over time. Because researchers looked at past medical records rather than carefully controlling a new study, other factors we don’t know about might have affected the results. The study didn’t include a group taking calcifediol without the diet, so we can’t be sure how much of the benefit comes from the supplement versus the diet. Finally, 84 people is a moderate sample size—a larger study would give more confidence in the results

The Bottom Line

If you have obesity and low vitamin D levels, ask your doctor about calcifediol supplementation combined with a Mediterranean-style diet. The evidence suggests this combination may help you lose more weight and reduce belly fat than diet alone or diet with regular vitamin D supplements. However, this is based on one study, so discuss with your healthcare provider whether this is right for your situation (moderate confidence level)

This research is most relevant for adults with obesity who have been diagnosed with vitamin D deficiency or insufficiency. It may be less relevant for people with normal vitamin D levels or those without obesity. Anyone considering supplements should consult their doctor first, especially if they take other medications or have kidney or bone health issues

Based on this study, you might expect to see meaningful changes in weight and belly fat within 3 months if you follow the diet and take calcifediol as prescribed. However, individual results vary, and it may take longer for some people. Vitamin D levels typically improve within 4-8 weeks of supplementation

Want to Apply This Research?

  • Track weekly weight and waist circumference measurements, plus a weekly photo of your midsection to visually monitor belly fat reduction. Also log your vitamin D supplement type and dose daily to ensure consistency
  • If using an app, set daily reminders to take your vitamin D supplement at the same time each day (consistency improves effectiveness). Log Mediterranean diet meals to ensure you’re following the eating plan, and track any hunger or energy level changes to monitor how you’re feeling
  • Measure and record weight and waist circumference weekly. Take progress photos monthly. After 3 months, ask your doctor to recheck your vitamin D blood levels to confirm improvement. Track energy levels, mood, and how your clothes fit as additional indicators of progress beyond the scale

This research describes the results of one study and should not replace professional medical advice. Before starting any vitamin D supplement, especially calcifediol, consult with your doctor or healthcare provider. This is particularly important if you have kidney disease, take certain medications, or have other health conditions. Vitamin D supplementation needs should be individualized based on your blood levels and health status. Results from this study may not apply to everyone, and more research is needed to confirm these findings.