Vitamin D and Thyroid Health
Vitamin D is a fat-soluble vitamin (technically a prohormone) essential for calcium and phosphate absorption, bone mineralisation, immune function, and muscle health.
Link to Thyroid Disease
- Many studies find that low vitamin D levels correlate with thyroid autoantibodies — the antibodies associated with autoimmune thyroid conditions like graves-disease.
- Some evidence suggests low vitamin D may correlate with features of thyroid cancer.
- Many people with hyperthyroidism have vitamin D deficiency, partly due to accelerated bone turnover and partly due to limited sun exposure.
- Results from studies are not all consistent, and evidence that supplementation improves thyroid function directly is limited.
Bone Health Connection
Hyperthyroidism accelerates bone turnover, risking bone-mineral-density loss. Vitamin D is essential for calcium absorption; deficiency compounds bone loss risk. See bone-mineral-density.
Sources of Vitamin D
Primary source: Sunlight on skin (UVB converts 7-dehydrocholesterol to vitamin D3)
Dietary sources (limited):
- Oily fish (salmon, tuna, sardines — also high in iodine)
- Mushrooms grown under UV light
- Milk and fortified dairy products
- Fortified cereals (check for iodine content)
- Egg yolks (also high in iodine — avoid on low-iodine-diet)
Supplementation
- NHS recommendation: All adults and children over 5 should take 10 mcg (400 IU)/day during autumn and winter.
- Consider year-round supplementation if: rarely outdoors, cover skin with clothing, have dark skin (melanin reduces UV-mediated synthesis), or live at high latitude.
- Vitamin D supplements do not interfere with levothyroxine absorption (unlike calcium and iron).