Top 3 Sources of Vitamin D
According to Harvard School of Public Health, an estimated one billion people of all ages and ethnicities have insufficient levels of vitamin D, 'the sunshine vitamin', in their blood. When our skin is exposed to the sun's rays, it triggers a chemical reaction that produces vitamin D3. There are many factors that influence the amount of sunlight that reaches the skin and its effectiveness. The time of day, season, altitude, clothing, sunscreen use, pigmentation and age are some of these factors. Even those that reside in a sunny climate can be deficient in vitamin D due to cultural traditions and/or dress (National Institute of Health). If you don't get out for a 15-minute walk in the sunlight every day, the odds are you're deficient. In a nutshell, we need this vitamin to:
- Promote calcium absorption
- Bone and muscle strength
A vitamin D deficiency may increase the risk of chronic diseases, including heart disease, osteoporosis, some cancers and multiple sclerosis, as well as contagious diseases such as and even the Sources of Vitamin D Dairy products and fatty fish The few foods that vitamin D is naturally present in includes the flesh of fatty fish, such as salmon, herring, tuna and mackerel. Beef liver, cheese and egg yolks contain small amounts. Breakfast cereals are manufactured to contain added vitamin D, along with some brands of yogurt, orange juice and other food products (National Institute of Health). The New England Journal of Medicine has a great table lists how much of this vitamin occurs in natural foods, fortified foods and supplements (page 270). 
Supplements Vitamin D is naturally present in very few foods so one of the best sources of it is supplements. The level in most multivitamins is too low (400 IU). You want at least 600 IU, which is more commonly found as a separate supplement. The National Institute of Health outlines how much Vitamin D and calcium is recommended depending on age. You can view the table here. This recommendation has sparked some controversy and is argued by one of the leading vitamin D researchers, Michael F. Holick, among others, that we should be consuming a lot more than we are now, with 800 to 1,000 IU per day being the minimum and more than 2,000 IU per day being ideal (see VITAMIN D: A D-LIGHTFUL SOLUTION FOR HEALTH). Cod Liver Oil By the late 1930s the use of Cod Liver Oil was widespread and was successful in eradicating significant health problems, including rickets. According to the New England Journal of Medicine, Cod Liver Oil contains between 400 - 1,000 IU of vitamin D3. In his paper Sunlight, vitamin D and Health: A D-lightful story, Michael F. Holick says;
"Cod liver oil is an excellent source whereas the flesh of cod and salted cod is not" - Michael F. Holick
Because Vitamin D is concentrated in the liver of the fish, it is abundant in cod liver oil. Fish oil on the other hand, is made from the whole body of the fish and has inferior levels of this vitamin. You can learn more about cod liver oil in our post Sources of vitamin D for mood support.
Sunlight and Your Health: An EnLIGHTening Perspective
Check out this energetic talk on the positive impacts of sunlight on your health by Michael F. Holick, PhD MD, of Boston University Medical Center. If you think you may be deficient in vitamin D, consider taking a supplement and including more foods that are rich in healthy omega-3 fatty acids in your diet.