Högskolan i Skövde

Vitamin D is essential for bone health, immune regulation, and muscle function. Exercise influences vitamin D metabolism, but the association between physical activity, gene expression, body composition, and other lifestyle and health factors remains unclear. This study aimed to investigate the relationships between body composition, circulating vitamin D levels, vitamin D receptor expression, and lifestyle factors assessed using a structured questionnaire, following a four-week exercise intervention. Four healthy women (aged 22–32) participated in an indoor exercise intervention, including cardio, resistance, and high-intensity interval training, performed five times per week. Body composition and physiological measures including body weight, body fat percentage and muscle mass were assessed using bioelectrical impedance analysis. Venous blood samples were collected pre- and post-intervention to measure Vitamin D levels and analyze VDR and PDIA3 gene expression using qPCR. Lifestyle habits such as sun exposure, diet, supplement use, and stress were assessed through a structured digital questionnaire conducted before and after the intervention. Results showed a slight, non-significant increase in vitamin D levels post-intervention, with individual differences likely influenced by lifestyle variables such as supplement use and sun exposure. Gene expression analyses revealed varied responses: one participant showed up-regulation of VDR and PDIA3, while others showed down-regulation, suggesting person-specific molecular adaptations. Body composition did not change significantly during the study. The findings suggest that even short-term exercise may influence vitamin D metabolism and related gene expression, although effects were limited and varied between individuals. Lifestyle habits appear to modulate both vitamin D status and molecular responses to exercise. For instance, the participant who consistently used vitamin D supplements showed the highest post-intervention vitamin D levels. Future studies with larger samples and longer durations are needed to clarify these relationships.

Popular scientific summary

Vitamin D, often referred to as the “Sunshine Vitamin” plays an important role in keeping us healthy. It helps our bones absorb calcium, supports the immune system, and is involved in muscle and heart function. Despite its importance, vitamin D deficiency is one of the most common nutrient problems in the world, affecting over one billion people. This is often due to poor diets, lack of sun exposure, and obesity.

While supplements and diet are commonly used to treat vitamin D deficiency, researchers are now exploring whether physical exercise could also help improve vitamin D levels and how well our bodies use it. Since vitamin D can be stored in fat and muscle, it is thought that exercise might help release it into the bloodstream and make our cells more responsive.

This study investigated the effect of a four-week exercise program on vitamin D levels in the blood and the expression of two important genes: the vitamin D receptor (VDR) and PDIA3. These genes help cells receive and respond to vitamin D, playing a key role in how the body uses this nutrient. Four healthy women aged 22 to 32 participated in a structured exercise program involving cardio, strength, and high-intensity interval training five times a week. Blood samples were collected before and after the four week exercise program to measure vitamin D levels and to analyze gene expression.

Participants also completed a lifestyle questionnaire about their sun exposure, diet, supplement use, sleep, stress level and physical activity habits. These responses provided context for understanding individual differences in the results. For example, the participant who regularly took vitamin D supplements had the highest post-intervention levels, while those with lower reported sun exposure or dietary intake showed smaller changes. These observations suggest that lifestyle habits may influence how the body responds to exercise in relation to vitamin D.

The results showed a small increase in vitamin D levels after the exercise period, but this change was not large enough to be considered significant. However, interesting effects were seen at the genetic level. Some participants showed increased expression of the VDR and PDIA3 genes after exercise, suggesting that their cells became more responsive to vitamin D. These results indicate that even if exercise does not immediately raise blood vitamin D levels, it might still improve how our bodies use the vitamin on a cellular level.

This study was small and short-term, which limits the ability to draw strong conclusions. All exercise was done indoors, so no sunlight exposure could influence vitamin D production. Despite these limitations, the findings contribute to our understanding of how exercise might support vitamin D function and overall health.

In summary, while a four-week exercise program may not be enough to significantly raise vitamin D levels in the blood, it could still help improve vitamin D function inside the body. More research with larger groups and longer exercise periods is needed. As vitamin D deficiency is very common, finding natural ways to improve vitamin D status could be important for public health.