What do mushrooms, eggs, milk, cheese, butter, oily fish (salmon, mackerel, tuna), caviar and liver have in common? They are all dietary sources of vitamin D.
Vitamin D actually refers to a group of related compounds that are soluble in fat and help us absorb and regulate calcium, magnesium, iron, phosphate and zinc. Vitamin D is also essential for healthy bones (it prevents osteomalacia and rickets), muscles, nerves, pancreas and immune function. Inadequate Vitamin D has been linked to an increased risk of multiple sclerosis (MS), Alzheimer’s disease, and possibly even diabetes. This doesn’t mean that low Vitamin D levels cause these diseases but it appears to play a role. It may also be useful in treating psoriasis.
The two forms of vitamin D that are most important to humans are Vitamin D2 (in mushrooms) and D3 (in animal products). However in order for Vitamin D (from food or sunlight) to perform its functions, it needs to be activated in the liver and kidneys. Therefore if you have liver or kidney disease, you may not be receiving the benefits of Vitamin D even with adequate sunlight and dietary intake. Also if you don’t eat any fat or oil with your mushrooms, and if you skim the cream off your milk, you won’t absorb the Vitamin D in them because it requires fat as a carrier. For these and other reasons that are not entirely clear, it is difficult to get our full quota of Vitamin D from dietary sources alone. We still need sunshine even if we eat a diet rich in foods that provide Vitamin D.
This highlights the interconnectedness of our foods and bodily systems. What appears to be Vitamin D deficiency could be a sign of poor liver or kidney function. This could then lead to calcium or other mineral deficiencies because of Vitamin D’s role in absorption of minerals.
Should you have a blood test to check your Vitamin D level? Should you take Vitamin D supplements (which usually contain the activated form of Vitamin D)? The evidence is inconclusive on both questions. Scientists have not come to a consensus about what blood level constitutes Vitamin D deficiency, and testing is not always accurate because of individual differences in skin colour and body fat composition. Supplement companies will tell you that most of the population is deficient and that Vitamin D will reduce your risk of cancer and lengthen your life. Some studies support this hypothesis; others do not. So what to do?
If you have no evidence of Vitamin D or mineral deficiencies, then I wouldn’t recommend testing or supplementing with Vitamin D tablets. Follow the sun exposure guidelines in my last HEB and eat a selection of the Vitamin D-containing foods in the photo (stir fry your mushrooms in butter, olive oil or coconut oil). If you have MS, Alzheimer’s, fragile bones, anaemia, psoriasis or liver/kidney disease, then I’d suggest visiting your doctor and discussing the possibility of testing and supplementing. Your doctor will evaluate your test results in the context of your personal medical history and be able to offer advice specific to your situation.