Vitamin D plays a crucial role in the regulation and use of calcium and phosphorus in the body. When we receive vitamin D from the sun or in the form of food, calcium absorption is increased in the small intestines. This helps in the formation and management of strong and healthy bones. Vitamin D also plays an important role in the immune system and influences cell growth.
Key Sources: Very few foods contain significant levels of vitamin D. Fatty fish are one, including salmon, herring, and mackerel, and fish liver oils such as cod liver oil. Meat, milk, and eggs may provide a lesser amount.
Plant-based sources include mushrooms, which may synthesise more vitamin D if placed in the sun for a few hours before cooking!
Vitamin D is unique in that it can be synthesised from the skin’s exposure to sunlight. Exposing hands, face, and arms to sunlight for 5-15 minutes, 2-3 times per week, generally provides adequate vitamin D.
Signs of Deficiency: Major deficiency signs are rickets, osteomalacia, osteoporosis, increased fracture risk, muscle weakness and pain. Also can contribute to immune and autoimmune conditions such as psoriasis, Hashimotos, increased susceptibility to colds and flu. Depression, especially seasonal affective disorder (SAD) has also been linked to deficiency.
Special Considerations: Dietary vitamin D is fat-soluble, so whether eating it in food or as a supplement, aim to have it with a source of fat. Animal sources of vitamin D are in the form 'D3', whereas plant sources are in the form 'D2'. D3 is better absorbed and converted into its active form much faster than D2.
Dark-skinned individuals, or those lacking sun exposure, are at greater risk of deficiency. The elderly are also an at-risk group, as the ability to synthesise vitamin D in the skin decreases with age, and actual time spent outside may decrease too – and supporting healthy bones at this time is more important than ever!
Nutrient Relationships: High intake of vitamin D can cause increased blood calcium, which in some cases may cause increased deposits in soft tissues and arteries. Vitamin K is vital for the body’s correct utilisation of calcium, therefore supplementing vitamin K alongside vitamin D may decrease the risk of harmful calcium deposits. Magnesium deficiency may impact vitamin D production in the body, and on the other side, high doses of vitamin D may have implications on magnesium levels. Therefore, combining magnesium with vitamin D should also be considered. Other cofactors for vitamin D are boron, zinc, and vitamin A.
Supplementing: During winter, or in other cases where sun exposure is reduced, a supplement is likely required as it is unlikely that food alone will meet demands. This is particularly relevant when a specific therapeutic dose of vitamin D is needed, e.g. for osteoporosis, immune deficiencies, or depression.
Babies usually can’t get adequate vitamin D from the sun, as their skin is too sensitive to be exposed to direct sunlight. In some cases, breastmilk may not provide enough vitamin D and supplementation may be required. This should be discussed with your healthcare practitioner.
- If you are strictly vegan, vitamin D2 in supplements is typically derived from yeast, whereas vitamin D3 is derived from lanolin in sheep’s wool.
- Vitamin D is fat-soluble and stored in the body. Therefore, toxicity is possible, so supplementation should be discussed with your healthcare practitioner.