How to Get Vitamin D in the Winter
Have you ever heard of the ‘sunshine vitamin’? No? You probably know it by its official name: Vitamin D. I want to talk to you about vitamin D and why you need it, especially during the darker days of fall and winter (more on this later). Read on as we break down the what, why and how to get Vitamin D for Dark Winter Months….it could make a huge difference in your health.
What is Vitamin D?
Vitamin D is a fat-soluble vitamin that serves several vital roles within the body. You can produce vitamin D naturally after exposure to the ultraviolet light rays in sunlight that trigger vitamin D synthesis. Otherwise, food and dietary supplements are other sources of the vitamin.The two main forms of vitamin D are vitamin D2 (ergocalciferol), found in plant foods, and vitamin D3 (cholecalciferol), found in animal based foods.
Functions of Vitamin D
Vitamin D plays a vital role for several processes within the body. These include:
-Bone health: Vitamin D is known for its role in aiding calcium absorption in the gut that helps promote bone formation. Without adequate vitamin D, the body is unable to effectively absorb calcium from the diet. The body will compensate for the missing calcium by pulling from the calcium stores within the existing bone. This process not only weakens the bones within the body, but affects the proper formation of new bone moving forward. Conditions such as rickets, osteomalacia (softening of the bone) and osteoporosis can be prevented with adequate vitamin D intake.
-Inflammation: Vitamin D has been the focus of research in regards to its role in reducing inflammation. Studies have found that higher levels of vitamin D are associated with lower levels of specific markers of inflammation (e.g. C-Reactive Protein). This has been observed with certain diseases such as arthritis, and some respiratory, gastrointestinal, and mental diseases.This may occur due to vitamin D’s ability to block the secretion of small, cell signaling proteins (cytokines) that are released as part of the body’s innate immune response. More research is needed to assess the exact mechanism of action, however multiple studies have observed the relationship between inflammation and vitamin D.
–Immune Function: Vitamin D is able to regulate the innate immune response and the autoimmune response due to the expression of a vitamin D receptor on immune cells.
-Cancer: Vitamin D is now recognized as playing a role in the prevention of cancer. This is due in part to Vitamin D’s ability to modulate cell growth, in this case preventing the uncontrolled cell growth of cancer cells.
–Mood and Depression: studies have shown that if you’re deficient in Vitamin D, you may be more susceptible to depression. If mental health and/or seasonal affective disorder (SAD) are a concern for you, making sure you’ve got enough Vitamin D could be critical.
Factors Affecting Absorption
With a nickname like the “sunshine vitamin” it is not surprising to know that vitamin D deficiency is a real issue during the fall and winter months when natural exposure to sunlight on bare skin is minimal. Further, some studies have indicated that in the fall and winter months, skin generates little to no vitamin D in states that are located in a northern latitude (37 degrees N, to be exact). For reference, this includes over half the United States including the area south of San Francisco, St. Louis and Richmond, VA.
Besides geographic latitude, other factors that can affect vitamin D absorption include:
- cloud cover
- sunscreen use
- time spent indoors
- clothing cover
- skin pigmentation
Essentially anything that can block the UV rays from reaching the skin lowers the absorption of vitamin D through the skin even in areas, and seasons, where rays are more direct.
Vitamin D Recommendations
The Institute of Medicine now recommends a dietary intake of 600 IU daily (or 800 IU if over the age of 70). There are limited dietary sources of vitamin D and many people end up supplementing. Keep in mind that many people may still experience low blood levels even when supplementing, so it is important to talk to your doctor about getting tested, continual monitoring, and the proper food sources, sun exposure and supplementation for your unique needs.
Carefully read nutrition labels and consider specific processing 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 ultraviolet 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.
Importantly, you CAN be too high in Vitamin D if you take too much from supplement sources so while some is good, more isn’t always better – like all supplements. Talk to your doctor to see if you should get your levels tested, monitored and possibly supplement this vitamin for optimal health. Many times, all you have to do is ask so consider getting it tested at your yearly physical with other blood tests like cholesterol.
Foods that contain vitamin D
Depending on the variety, studies show that salmon (especially wild varieties) contributes ~450-950 IU vitamin D per 3 ounce serving.
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
Cod liver oil is more often used as a dietary supplement than a commonly consumed food on its own. If it is medically indicated, just a small portion of one tablespoon contributes ~1300 IU of vitamin D.
Don’t ditch that 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 of the vitamin, it is not indicated to eat enough eggs daily to get all of your vitamin D from this source.
Some mushrooms grown in ultraviolet light contribute vitamin D2 (ergocalciferol). Brands containing vitamin D will be marked as such since many types of mushrooms are grown in the dark and therefore will not be considered a vitamin D source. Find a brand grown in light for ~400 IU vitamin D in 3 ounces of diced mushrooms.
Fortified Milks (dairy and non-dairy)
Dairy milk and yogurts have been fortified with 100 IU per 8-ounces since the 1930’s. Many, but not all, non-dairy or plant-based milks are fortified, so read labels carefully on any type of milk to be sure you are getting a fortified product.
Fortified orange juice
Many, but not all, packaged orange juices are fortified with vitamin D in levels similar to fortified milks (8-ounces contribute ~100 IU). They are also fortified with calcium. Keep in mind that freshly squeezed juices do not contribute vitamin D to the diet so read the labels of any juice package to verify that it is a fortified product.
Ginger Hultin,MS, RD, CSO
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