By Georgia Hartmann
Women's health specialist
Deficiency in vitamin D, a fat-soluble vitamin, is estimated to affect more than one billion people worldwide.
As 50-90% of vitamin D is absorbed through the skin via sunlight, the problem we face is that many people do not spend sufficient amounts of time in direct sunlight.
Vitamin D for Immune Function
While vitamin D was first recognised for its role in bone mineralisation and calcium regulation (rickets is a bone disease characterised by vitamin D deficiency), more recently it is known to exert many extra-skeletal effects including modulating the immune system.
Vitamin D has numerous effects on cells within the immune system. It inhibits the proliferation of particular immune cells一B cells, which produce antibodies, and T cells which (when unbalanced) promote inflammation. Ultimately, this results in decreased production of inflammatory proteins (called cytokines).
Because of this positive impact, vitamin D is commonly investigated and used in the management of autoimmune diseases including type 1 diabetes, multiple sclerosis, inflammatory bowel disease, systemic lupus erythematosus, and rheumatoid arthritis.
Vitamin D for Thyroid Disorders
Vitamin D has also been studied for its beneficial role in improving thyroid disorders, including hypothyroidism and autoimmune thyroid disorders including Hashimoto’s.
In fact, one case-control study found vitamin D deficiency in 92% of patients with Hashimoto’s disease.
Supplementation with vitamin D has also been shown to reduce thyroid antibodies in Hashimoto’s disease, namely thyroid peroxidase antibodies.
A recent randomised-control trial found that hypothyroid patients who supplemented with vitamin D for 12 weeks improved their Thyroid Stimulating Hormone (TSH) and calcium concentrations, overall improving thyroid function.
You need sunlight for Vitamin D
Unlike other essential vitamins that are obtained from food, vitamin D is absorbed mostly from sunlight exposure to the skin. Though, the presence of clothing, excess body fat, sunscreen, and the skin pigment melanin each affect how well vitamin D is absorbed.
Here is a general guide on vitamin D absorption, depending on your skin type: