Vitamin Dз in foods is found mostly in fish oils. It can also be made synthetically by ultraviolet light irradiation of a derivative of cholesterol. Vitamin D2 is a different synthetic form, known as ergocalciferol. The Vitamin D added to milk, a practice begun in the 1930's to prevent rickets, can be either one of those two synthetic forms. However, according to studies published in the New England Journal of Medicine in 1991 and 1993, seven out of ten samples of milk contained less than 80% of the amount listed on the label, five didn’t even have 50%, and 14% of the skim milk samples had no Vitamin D at all.
Cod Liver Oil is the classic Vitamin D source that has been used for generations in Northern Europe, where there is little sun and therefore much less opportunity to obtain this nutrient.
HOW TO INCREASE VITAMIN D INTAKE FROM FOODS
1) Grind a teaspoon to tablespoon of flax seeds in a coffee or spice grinder once a day. Add just before serving to porridges, grains, breads, or even drinks. According to Paul Stitt, a biochemist and author of Beating the Food Giants, the regular consumption of flax seeds increases vitamin D levels as well as the retention of calcium, magnesium, and phosphates, which is all good news for the bones.
2) Consume wild ocean fatty fish such as mackerel and salmon (make sure to eat the skin!), as well as caviar or fish eggs. Try salmon caviar or the Greek taramasalata; two or three servings per week are quite sufficient.
3) If you have little exposure to the sun, in whatever season, don’t neglect cod liver oil. A teaspoon per day should be enough.
4) There are vitamin D precursors in plant foods and leafy greens, known as ergosterols; parsley is a particularly rich source. So are mushrooms. I found from my nutritional software (ESHA Research) that 1½ ounces cooked shiitake mushrooms contain 69% of the vitamin D RDA’s for a 55-year old woman).
So -- eat lots of fatty ocean fish, parsley, and shiitake mushrooms, take a walk in the sun, and use plenty of good quality olive oil and other healthful fats to keep enough vitamin D in your body for your health and wellbeing!