Researchers looked at 28 different studies involving 1,675 adults to see if taking vitamin D supplements while exercising was better than just exercising alone. They found that vitamin D supplements did increase vitamin D levels in the blood, which is good. However, adding vitamin D didn’t help people lose more fat or weigh less than exercise alone. The good news? Vitamin D supplements did help a little bit with certain types of strength, especially in older adults and people taking higher doses. So while vitamin D is important for health, exercise appears to be the real star when it comes to changing your body composition.

The Quick Take

  • What they studied: Whether taking vitamin D pills while exercising helps adults build more muscle and lose more fat compared to just exercising without vitamin D
  • Who participated: 1,675 adults across 28 different research studies. The studies included both healthy people and those with health conditions, ranging from younger to older adults
  • Key finding: Adding vitamin D to an exercise routine successfully raised vitamin D blood levels, but didn’t help people lose more weight or fat compared to exercise alone. However, it did provide small improvements in certain strength tests, especially for older adults
  • What it means for you: If you’re exercising to change your body shape or lose weight, the exercise itself is doing most of the work. Vitamin D supplements may help a little with strength gains, particularly if you’re older or taking higher doses, but they won’t replace the benefits of regular exercise

The Research Details

This was a meta-analysis, which means researchers gathered and combined results from 28 different studies that had already been completed. Each of these studies compared two groups of adults: one group that took vitamin D supplements while exercising, and another group that exercised without vitamin D. The researchers searched three major scientific databases (PubMed, Web of Science, and Scopus) for all studies published up until April 2024 that looked at this specific question.

The researchers then looked at what happened to several measurements in these studies: vitamin D blood levels, body weight, BMI (a measure of weight relative to height), fat mass, body fat percentage, muscle mass, and strength in different areas like grip strength and leg strength. They used special statistical methods to combine all the results and look for patterns across all the studies.

This approach is powerful because it combines information from thousands of people across many different studies, which gives a much clearer picture than any single study could provide. The researchers also looked at whether the amount of vitamin D used or how long people took it made a difference in the results.

By combining results from many studies, researchers can see the true overall effect of vitamin D supplements with exercise. Individual studies might show different results due to chance or differences in how they were done, but when you combine them all together, you get a clearer answer. This type of analysis is especially important for nutrition questions because people’s bodies respond differently, and it takes many studies to find the real pattern

This study is a high-quality analysis because it included 28 different randomized controlled trials (the gold standard for research), involved over 1,600 participants, and searched multiple scientific databases to find all relevant studies. The researchers registered their plan ahead of time (PROSPERO registration), which helps prevent bias. However, the individual studies included may have had different quality levels, and some results showed variability between studies, which means not all findings are equally strong

What the Results Show

The most clear-cut finding was that vitamin D supplements successfully increased vitamin D levels in the blood by about 34 nanomoles per liter more than exercise alone. This happened in both healthy adults and those with health conditions, showing that the supplements were working as intended.

When it came to body composition (how much fat versus muscle you have), the results were disappointing for those hoping vitamin D would be a magic bullet. Adding vitamin D to exercise didn’t help people lose more weight, reduce their BMI, lose more fat, or gain more muscle compared to just exercising without vitamin D. All of these results were not statistically significant, meaning the differences were too small to be meaningful.

For strength, the picture was more mixed. Overall, vitamin D didn’t significantly improve strength across all the studies. However, when researchers looked more closely at specific types of strength tests, they found modest improvements in knee extension strength (the strength used to straighten your leg) of about 4.36 kilograms. Handgrip strength also improved, particularly in older adults and in people who took higher doses of vitamin D.

An important secondary finding was that the benefits of vitamin D appeared to be dose-dependent, meaning higher doses seemed to work better than lower doses. Older adults appeared to benefit more from vitamin D supplements than younger adults, particularly for handgrip strength. This suggests that age and the amount of vitamin D taken may influence how much benefit someone gets from supplementation

This research aligns with previous findings that exercise is the primary driver of body composition changes and muscle building. The modest improvements in certain strength measures are consistent with vitamin D’s known role in muscle function, but the lack of major body composition changes suggests that vitamin D alone cannot replace the effects of good exercise programming. The findings support the idea that vitamin D is important for overall health and may support strength in specific ways, but it’s not a shortcut to fitness goals

The studies included had different designs and quality levels, which can affect the overall results. Some studies were short-term, so we don’t know if benefits would continue over years. The studies used different amounts of vitamin D and different types of exercise, making it harder to pinpoint the exact best approach. Additionally, most participants were already relatively healthy, so results might be different for people with serious vitamin D deficiencies or certain medical conditions. The researchers couldn’t account for all differences between studies, and some results showed more variation than others, suggesting the effects might not be consistent for everyone

The Bottom Line

If you’re exercising to improve your body composition or build muscle, focus on consistent, quality exercise as your main tool—that’s where the real results come from (high confidence). If you have low vitamin D levels or are at risk for deficiency (especially if you’re older, live in a northern climate, or have limited sun exposure), vitamin D supplementation is worth discussing with your doctor for overall health benefits (high confidence). If you’re older and interested in maintaining or improving strength, vitamin D supplementation combined with exercise may provide modest additional benefits beyond exercise alone, particularly at higher doses (moderate confidence). Don’t expect vitamin D supplements to significantly change your weight or body fat percentage on their own (high confidence)

Older adults should pay special attention to these findings, as they showed the most benefit from vitamin D supplements for strength. Anyone with known vitamin D deficiency should consider supplementation for overall health. People focused on losing weight or changing body composition should understand that exercise is the key factor, not vitamin D. Athletes and fitness enthusiasts might find modest strength benefits from vitamin D, especially at higher doses. People with certain health conditions that affect vitamin D absorption should discuss supplementation with their healthcare provider

If you start taking vitamin D supplements, blood levels typically increase within weeks (2-4 weeks). However, improvements in strength may take longer—expect to see changes over months (8-12 weeks) of consistent exercise combined with supplementation. Changes in body composition (fat loss or muscle gain) primarily depend on exercise and diet, not vitamin D, so focus on those factors for visible changes within 4-8 weeks

Want to Apply This Research?

  • Track weekly strength measurements in specific exercises (handgrip strength using a grip dynamometer, or leg press/knee extension weights) alongside vitamin D supplementation dose and exercise frequency. Record measurements every 2-4 weeks to monitor for modest improvements over time
  • Set a daily reminder to take your vitamin D supplement at the same time each day (such as with breakfast), and log it in the app. Pair this with logging your exercise sessions to see the combined effect. If you’re older or taking higher doses, track grip strength monthly using a simple grip strength test to monitor for improvements
  • Create a long-term tracking dashboard showing: (1) daily vitamin D supplementation adherence, (2) weekly exercise frequency and type, (3) monthly strength measurements in 2-3 key exercises, and (4) quarterly body composition checks (weight, body fat percentage if available). This helps identify patterns and whether the combination is working for your individual goals

This research summary is for educational purposes only and should not replace professional medical advice. Before starting vitamin D supplements or changing your exercise routine, consult with your healthcare provider, especially if you have existing health conditions, take medications, or are pregnant or breastfeeding. Individual results vary, and what works for the average person in research studies may not apply to your specific situation. This analysis represents current research findings but does not constitute medical treatment recommendations.