Vitamin D: A Key Player in Immune Function and Energy Metabolism

Vitamin D: A Key Player in Immune Function and Energy Metabolism Vitamin D deficiency is estimated to affect approximately 1 billion people worldwide, with nearly half the global population experiencing vitamin D insufficiency. We know seasonality and daylight hours have a significant impact, but deficiency is also more prevalent in the elderly, individuals living with obesity, individuals with higher melanin content in the skin, and those who spend a large amount of time indoors or with skin highly covered.

Vitamin D deficiency is estimated to affect approximately 1 billion people worldwide, with nearly half the global population experiencing vitamin D insufficiency. We know seasonality and daylight hours have a significant impact, but deficiency is also more prevalent in the elderly, individuals living with obesity, individuals with higher melanin content in the skin, and those who spend a large amount of time indoors or with skin highly covered.

Vitamin D is found in only a few foods, including whole-fat milk, fatty fish and mushrooms. The majority of our intake typically occurs through sun exposure, specifically UVB rays, where vitamin D is synthesised in the skin. Two enzymatic reactions then occur in the liver and kidneys to create the biologically active form of vitamin D.

In clinical practice, it’s not always obvious to pick up on vitamin D deficiencies, as many patients present asymptomatically. However, the implications of chronic vitamin D deficiency can be severe, including:

Reduced intestinal calcium and phosphorus absorption which can lead to hypocalcemia and/or secondary hyperparathyroidism
Accelerated bone demineralisation and increased risk for osteomalacia and osteoporosis
Increased susceptibility to some infections and potentially an increased risk for autoimmunity in those who are genetically susceptible
Increased association with anxiety and depressive symptoms

The functions of vitamin D are widespread throughout the body, with the active form being known to induce the transcription of over 900 genes. Vitamin D is widely recognised for its role in bone health, and more recently; its critical influence on immune regulation, inflammation, and mitochondrial energy production. Let’s further explore the impact of vitamin D on immune function and energy metabolism.

Vitamin D and the Immune System

Vitamin D impacts both the innate and adaptive immune responses, influencing various immune cells, including macrophages, dendritic cells, and B and T lymphocytes. Additionally, the active form, calcitriol (1,25-dihydroxyvitamin D), binds to vitamin D receptors on immune cells, enhancing antimicrobial peptide production, such as cathelicidins and defensins, which help defend against infections by disrupting bacterial membranes.

There is emerging epidemiologic evidence to suggest that vitamin D deficiency may increase the risk of developing some autoimmune conditions and/or accelerate the progression. Low vitamin D status is often more prevalent in those with autoimmune conditions, but more research is required to better understand the underlying mechanisms behind this.

Furthermore, vitamin D plays an important role in regulating inflammatory pathways. The effects of vitamin D on immune cells result in reduced output of pro-inflammatory cytokines, such as TNF-alpha and IL-6, while promoting anti-inflammatory cytokines, and inhibiting dendritic cell maturation, which promotes immune tolerance rather than excessive immune activation.

The Role of Vitamin D in Energy Production

Beyond its role in immune function and bone health, vitamin D is also involved in energy production and mitochondrial health. Vitamin D deficiency may reduce mitochondrial respiration, thereby influencing ATP production and energy metabolism. There is emerging evidence to suggest that vitamin D supplementation may assist with both mitochondrial function and density.

Vitamin D deficiency has been linked to fatigue, muscle weakness, and decreased exercise performance, which may be partially explained by mitochondrial dysfunction and increased oxidative stress. Vitamin D deficiency may also be associated with increased skeletal muscle atrophy over time.

Clinical Considerations for Practitioners

When assessing vitamin D status in clients, several factors should be considered:

Serum 25(OH)D Testing: the most accurate biomarker for vitamin D status is serum 25-hydroxyvitamin D.
Dosing and Supplementation: individual requirements vary based on unique health circumstances, sun exposure, dietary intake and current vitamin D status. While international guidelines vary, for most countries the RDA for vitamin D is around 600–800 IU per day. Individuals with deficiencies and/or increased risk factors may require significantly higher daily intakes.
Form: Cholecalciferol is the most commonly supplemented form, and also the same form that is produced in skin upon exposure to sunlight. Enzymatic reactions in the liver and kidneys then convert this to the active form, calcitriol. Calcifidiol is a more active metabolite that can raise vitamin D levels more rapidly and predictably, particularly in individuals with liver or absorption challenges.
Co-factors for Absorption: magnesium is required for the activation of vitamin D, and consuming dietary fat alongside vitamin D supplements assists with the absorption.
Seasonal Considerations: Vitamin D levels typically decline during winter months due to reduced UVB exposure, increasing the need for supplementation.

Conclusion

Vitamin D is a secosteroid hormone with various functions throughout the body. As a modulator of immune resilience and mitochondrial efficiency, optimising vitamin D status may play a pivotal role in preventing infections, reducing inflammation, and enhancing cellular energy production. By integrating evidence-based strategies to assess and address vitamin D levels, practitioners can support clients in achieving a robust immune system and sustained vitality.

About the writer,

Nicole Freebairn

Nicole is a Registered Nutritionist and Recipe Writer with a background in clinical nutrition, specialising in weight management and metabolic health. Her expertise in these areas ensures that her guidance is both practical and rooted in the latest scientific research.

Disclaimer: The information presented in this article is intended solely for educational purposes and is not a substitute for personalised medical advice. Nutrient and supplement recommendations may differ based on individual health conditions and needs. Health practitioners should conduct thorough research and consult reliable sources before advising clients on new supplements, ensuring any potential interactions with medications are carefully evaluated.

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