As the weather turns darker and we head into winter, be aware that, without natural exposure to sunlight on bare skin, vitamin D deficiency is a real issue. Some studies have indicated that in the fall and winter months, skin generates little to no vitamin D above 37 degrees north. For reference, that’s more than half the United States, including the area south of San Francisco, St. Louis and Richmond, VA. Factors such as geographic latitude, cloud cover, sun block, time spent indoors, clothing cover and skin pigmentation can lessen the absorption of vitamin D even in areas where rays are more direct. The Institute of Medicine is now recommending a dietary intake of 600 IU daily (or 800 IU if over the age of 70).
Aside from its role regarding calcium absorption in the gut, vitamin D is known for preventing both rickets and osteomalacia, helping to prevent osteoporosis. It also modulates cell growth and plays vital roles in immune function, gene coding and reducing inflammation. Vitamin D is now recognized as playing a role in cancer and auto-immune protection. As we head into the darker months, be sure to include sources of dietary vitamin D. Read labels and consider specific processing carefully to be sure you really are getting a true vitamin D source in your food. For example, not all mushrooms contain vitamin D; they must be grown with ultra-violet light and will be marked as such to ensure they are a vitamin D source. Not all non-dairy milks or orange juice are fortified so be sure to read labels. Talk to your doctor to see if you should get your levels tested and possibly supplement this vitamin for optimal health.
Foods that contain vitamin D
Salmon: Depending on the variety, studies show that salmon (especially wild salmon) contributes ~450-950 IU vitamin D per 3-oz. serving.
Canned tuna: Tuna varieties contain differing amounts of vitamin D, but the most convenient and affordable option is tuna canned in water. A 4-oz. can contributes ~150 IU vitamin D.
Cod liver oil: More often used as a dietary supplement than a food, if cod liver oil is medically indicated, a small portion of one tablespoon contributes a large portion of vitamin D at ~1,300 IU.
Whole eggs: Don’t ditch the yolk! Fat-soluble vitamins are contained in the yolk of an egg, which contributes a small amount of dietary vitamin D at ~40 IU each. However, at such a low level , it is not indicated to eat enough eggs daily to get all of your vitamin D from this source.
Mushrooms: Some mushrooms grown in ultra-violet light contribute vitamin D2 or ergocalciferol. Brands containing vitamin D will be marked as such since many types of mushrooms are grown in the dark and therefore not considered a vitamin D source. Find a brand grown in light for ~400 IU vitamin D in a 3-oz. portion.
Fortified milks, both dairy and non-dairy: Dairy milk and yogurts have been fortified with 100 IU per 8-oz. since the 1930s. Many, but not all, non-dairy or plant-based milks are also fortified. Read labels carefully to be sure you are getting a fortified product.
Fortified orange juice: Not all packaged orange juices are fortified with vitamin D in levels similar to fortified milks (8 oz. contributes ~100 IU). They are also fortified with calcium. Keep in mind that freshly squeezed juices do not contribute vitamin D to the diet. Read the labels of any juice package to verify that it is a fortified product.