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Why do we need Vitamin D?
Some nutrient sources contain dense amounts of Vitamin D3, and it can be acquired in significant amounts by including them in one’s diet, though in many instances the amounts would probably fall below recommended levels. This is partly because during the course of evolution in Equatorial zones, skin exposed to solar radiation became the principal way of humans acquiring it, rather than through our diet. Furthermore not all Vitamin D is actually absorbed when it is eaten. It’s absorption is mainly at the distal (far) end of the large intestine. Vitamin D is mainly stored in the liver and kidneys of mammals, but not for long periods of time. Predatory carnivores like wolves and cats, as well as human beings who, until the advent of agriculture, were also predators, can acquire Vitamin D from consuming the organs of prey animals. Humans were (and are) also food collectors of bird eggs and mushrooms, which are also good sources of Vitamin D.
Sources of Vitamin D3 in food
The highest concentrations of D3 are found in oily fish. It accumulates in fish livers after becoming concentrated through the food chain, beginning with algae and moving up through small fish eaten by larger fish that are in turn eaten by ever larger fish. Cod liver oil is the densest nutrient source available at reasonable cost. And oily fish, especially salmon, are also an excellent and widely available source.
Sardines, herring, mackerel, swordfish, trout and tuna also supply significant amounts of Vitamin D. The extra benefit from all these fish are that they contain Omega 3 fatty acids, a potent fat with many additional health benefits. Sardines, herring and baby mackerel are also eaten whole and so their small bones can also increase calcium intake.
Vegans as well as other vegetarians can rely on many mushrooms for some of their vitamin D. Shiitake mushrooms hold significant quantities and are a source of protein as well. Even less costly portobello mushrooms also contain useful amounts of D and are widely available.
Food Preparation to minimize loss of Vitamin D
How these foods are prepared is important in order to maximize the dose received. Frying fish in oil reduces the Vitamin D available because it is a fat soluble vitamin–and can be dissolved all along the cooking surface of the fish where it is taken up by the oil in which it’s cooked. Steamed, baked or broiled fish retain more Vitamin D. Higher temperatures can destroy some vitamin D too, but if the fish is steamed, the temperature never exceeds that of boiling water and all the benefits, as well as the taste of the fish, are retained.
Cow’s milk is widely fortified with Vitamin D (as are many processed foods). Vitamin D fortification in developed countries was undertaken as an inexpensive and effective way to prevent “Rickets” which is a serious disorder of bone development mainly found in children, especially those who are desperately poor. Vitamin D is also found in significant amounts in milk from dairy herds that rely on pasture for forage. It is present in new-mown hay because it’s produced by dying and drying plants, specially alfalfa. Animals that consume large amounts of such forage produce milk with Vitamin D3 in higher amounts than those fed other types of feed in barns. Importantly cow’s milk is fortified with D3–so a true benefit is derived. Fortification is an inexpensive and effective way for public health campaigns to help all people to avoid the most serious vitamin D deficiencies, particularly rickets. However, eating many processed foods to gain vitamin D is not a good idea because many of these possess a long list of other far less desirable attributes.
Dietary acquisition of vitamin D may be problematic for many individuals due to dietary restrictions associated with biological and cultural sensitivities including: vegetarianism (either as a religious or ethical stance), lactose intolerance related to aging or the basic physiology of most of the global population, and dietary restrictions related to other health issues and medical treatments. Dietary supplementation with Vitamin D3 is recommended for nearly all people who do not spend significant amounts of time exposed to the sun. That means most of us.