Can You Lose Vitamin D Through Exercise? Separating Fact from Fitness Myths

October 23, 2025 •

4 min read

According to a recent study from the University of Bath, regular indoor exercise can significantly mitigate the seasonal decline in vitamin D levels among overweight and obese adults. This exciting finding directly counters the misconception that you can lose vitamin D through exercise, revealing a more beneficial relationship between fitness and the 'sunshine vitamin.'

Quick Summary

Exercise does not cause a loss of vitamin D. Instead, physical activity can help maintain levels by prompting the release of vitamin D from fat and muscle tissue stores.

Key Points

Exercise doesn't deplete vitamin D: As a fat-soluble vitamin, vitamin D is stored in body fat and muscle, not excreted through sweat like water-soluble vitamins.
Workouts mobilize vitamin D stores: Physical activity, especially intense exercise, triggers lipolysis and causes the release of vitamin D from tissue reserves into the bloodstream.
Indoor exercise helps maintain levels: Studies show that regular indoor exercise can effectively mitigate the seasonal decline in vitamin D concentrations, even without sun exposure.
Outdoor exercise provides a double benefit: Exercising outdoors combines the metabolic advantages of physical activity with sun-induced vitamin D synthesis, leading to the greatest overall increase.
Athletes can still be deficient: Despite high activity levels, factors like increased utilization, extensive indoor training, and low body fat can put athletes at a higher risk of vitamin D deficiency.
Listen to your body: If you experience excessive head sweating, persistent fatigue, or muscle weakness, it could be a sign of low vitamin D, and you should consult a healthcare professional.

Debunking the Myth: The Fat-Soluble Reality

Contrary to popular belief, you cannot lose vitamin D through sweat or exertion. The idea likely stems from general concerns about nutrient loss during intense physical activity, but it misinterprets how the body handles different types of vitamins. While water-soluble vitamins like B and C can be lost through sweat, vitamin D is fat-soluble. This means it is stored in the body's fat and muscle tissue, not readily flushed out during a workout. The true story of exercise's impact on vitamin D is far more interesting and positive.

The Surprising Ways Exercise Improves Vitamin D Metabolism

Rather than causing a loss, physical activity appears to have a dynamic and beneficial relationship with vitamin D metabolism. The primary mechanisms involve the mobilization of existing stores and improved overall regulation.

Mobilization of Vitamin D Reserves

Intense exercise triggers lipolysis, the process of breaking down fats for energy. Since vitamin D is stored in adipose (fat) tissue, this process can lead to the release of stored vitamin D metabolites into the bloodstream, increasing circulating levels. Some research indicates that skeletal muscle tissue also acts as a reservoir, releasing 25(OH)D3, a precursor form of vitamin D, into circulation after a workout. A study in young soccer players found that a single intense exercise session significantly increased serum 25(OH)D3 concentrations, supporting the hypothesis that muscles can both store and release vitamin D.

Enhanced Hormonal Regulation

Exercise influences several hormones involved in vitamin D regulation, including parathyroid hormone (PTH). When an acute bout of exercise causes a transient increase in PTH, it can stimulate the conversion of 25(OH)D to its active form, 1,25(OH)2D, a process that helps maintain calcium homeostasis. Regular training can also influence the expression of enzymes and receptors, such as the Vitamin D Receptor (VDR), within muscle tissue, potentially leading to better local utilization of vitamin D.

The Confounding Factor of Outdoor Activity

For those who exercise outside, the biggest benefit comes from sun exposure, which is the body's primary source of vitamin D. The physical activity itself is less of a direct factor in the increase, although it is likely to correlate with more time spent outdoors. Numerous studies show that outdoor exercise is strongly associated with higher vitamin D levels, highlighting the importance of sun exposure. In fact, a systematic review found that while exercise outdoors significantly increased vitamin D levels, the effect of indoor exercise was minimal unless accompanied by weight loss.

Indoor vs. Outdoor Exercise on Vitamin D

While sun exposure is a powerful component, indoor exercise can still provide metabolic benefits for vitamin D. A 2025 study found that overweight and obese adults who followed a 10-week indoor exercise program saw significantly smaller drops in their vitamin D levels during winter compared to a non-exercising group. This suggests that even without sun, the metabolic effects of exercise can help preserve vitamin D stores.


Feature	Indoor Exercise	Outdoor Exercise
Sunlight Exposure	None (unless near window)	High (dependent on time/location)
Primary Mechanism	Mobilization of tissue stores (lipolysis)	Both sun-induced synthesis and metabolic mobilization
Effect on Vitamin D	Mitigates seasonal decline	Significantly boosts overall levels
Dependency	Relies on existing fat/muscle reserves	Relies on immediate sun exposure and existing reserves
Typical Setting	Gym, home workouts, studio classes	Running, cycling, sports in open air

Risk Factors for Athletes with Vitamin D Deficiency

Interestingly, a high prevalence of vitamin D deficiency is found in athletes, even those who train outdoors. This phenomenon can be attributed to several factors:

Increased Utilization: Intense exercise may increase the body's metabolic demand for vitamin D, depleting reserves more quickly.
Indoor Training: Many athletes spend significant time training indoors, especially during off-season or in specific sports, limiting sun exposure.
High Latitude and Season: Training during winter or in regions with limited sunlight reduces natural production.
Low Body Fat: Athletes with very low body fat may have fewer reserves to mobilize.

Practical Steps to Boost Vitamin D Levels

To optimize your vitamin D status, consider the following strategies:

Balanced Exposure to Sunlight: Spend 10–20 minutes outdoors in direct sunlight on most days, particularly if you live in a higher latitude. Be mindful of skin cancer risk and don't overdo it.
Dietary Sources: Include fatty fish like salmon and mackerel, fortified dairy products and cereals, egg yolks, and mushrooms in your diet.
Regular Exercise: Maintain a consistent exercise routine, whether indoors or outdoors. The metabolic benefits can help manage existing vitamin D levels.
Consult a Professional: If you are concerned about deficiency, speak to your doctor or a registered dietitian. They can recommend a blood test and, if necessary, a supplementation plan.
Understand Your Body: Pay attention to factors like geographic location, skin tone, and body composition, as these all influence vitamin D production and absorption.

Conclusion: Exercise is a Friend, Not a Foe, to Vitamin D

The concern that exercise can cause you to lose vitamin D is a myth. Instead, physical activity is a helpful ally in maintaining and regulating your body's vitamin D levels. While outdoor exercise offers the added benefit of sun-induced synthesis, even indoor workouts provide metabolic advantages by encouraging the release of vitamin D from its storage sites. For athletes and anyone with potential deficiency risks, combining regular exercise with proper nutrition and smart sun exposure is a powerful strategy. Instead of worrying about depletion, embrace your workouts as a tool to support your overall vitamin D health.

For more detailed information on the exercise-vitamin D link, explore the systematic review on the effect of physical activity on vitamin D by ScienceDirect.

Frequently Asked Questions

No, sweating does not remove vitamin D from the body. Vitamin D is a fat-soluble vitamin stored in your fat and muscle tissue. Sweat primarily consists of water and electrolytes, not fat-soluble nutrients.

Working out indoors does not cause a deficiency, but it eliminates the primary source of natural vitamin D production: sunlight. However, some studies show that indoor exercise can help preserve existing vitamin D stores.

Yes, outdoor exercise can significantly increase vitamin D levels, but this is primarily due to increased sun exposure, not the exercise itself. The combination of sun and exercise offers the greatest benefit.

Athletes may have low vitamin D levels for several reasons, including increased metabolic demand, extensive indoor training, low body fat, and training during winter months.

Excessive sweating, particularly on the head, is recognized as a potential sign of vitamin D deficiency, although it can be caused by other factors.

It is best to consult a doctor before starting any supplement regimen. They can determine if you have a deficiency and recommend the appropriate dosage. A combination of diet, sun exposure, and exercise is generally most effective.

Intense exercise causes the body to break down fat for energy (lipolysis), which in turn releases fat-soluble vitamin D and its metabolites into the bloodstream. Skeletal muscle also plays a role as a storage site.