Vitamin D is an essential, fat soluble vitamin. This means that we need to consume it in our diets and lifestyle as our bodies do not make it. This also means that we need to consume fat in order to absorb Vitamin D.
Vitamin D is used for many bodily functions, including;
Building and maintaining healthy bones
Supports your immune system
Aids in muscle function
What are some sources of Vitamin D?
Fortified Foods such as soy, dairy, and orange juice
See this chart from the USDA for exact amounts of Vitamin D in foods.
Vitamin D isn't naturally found in many foods, but you can get it from fortified milk, fortified cereal, and fatty fish such as salmon, mackerel and sardines. Your body also makes vitamin D when direct sunlight converts a chemical in your skin into an active form of the vitamin (calciferol). The amount of vitamin D your skin makes depends on many factors, including the time of day, season, latitude and your skin pigmentation. Depending on where you live and your lifestyle, vitamin D production might decrease or be completely absent during the winter months. Sunscreen, while important to prevent skin cancer, also can decrease vitamin D production. Many older adults don't get regular exposure to sunlight and have trouble absorbing vitamin D. If your doctor suspects you're not getting enough vitamin D, a simple blood test can check the levels of this vitamin in your blood.
There are two types of Vitamin D:
Cholecalciferol (D3)- Found in Animal Products
Ergocalciferol (D2)- Found in Plants
Vitamin D3 (Cholecalciferol) has been proven to be more effective in treating Vitamin D deficiencies than Vitamin D2. However there are now synthetically produced Vegan Vitamin D3 supplements that contain Lichen and are as effective as animal derived D3 options.
Vitamin D in a Plant-Based Diet
When following a plant-based diet the only sources of vitamin D to consume are from sunlight, mushrooms, and fortified foods. Depending on your location and the amount of mushrooms and fortified foods you are eating on a regular basis, it is safe to say that at least for a few months out of the year you are likely to be at risk for a Vitamin D deficiency. This is also true for non-plant-based eaters as if you are not regularly consuming fatty fish or receiving adequate sun you may also be at high risk for deficiency. To combat this I suggest during the darker/ winter months doing the following:
Taking a supplement (after getting your levels checked/speaking with your healthcare provider)
Eating fortified foods such as tofu, soy milk, almond milk, and cereals regularly
Eat lots of mushrooms!
Here are a few of my favorite mushroom-packed recipes that I have created!
How much do we need?
The Recommended Dietary Allowance (RDA) for vitamin D is:
400 IU for children <12 months
600 IU for people <70 years old
800 IU for those over >70 years old
Now here is the tricky part. It is much more important how much vitamin D that makes it into your bloodstream than the actual amount you're consuming. So if you may not need to supplement with the highest amount if you are absorbing and using the majority of it. So checking your blood levels is important to see how much you are actually utilizing. Vitamin D blood levels above 20 ng/ml are considered adequate for maintaining healthy bones and anything below that should begin supplementing.
How does Vitamin D work in our bodies?
When we get vitamin D from the sun it is produced endogenously when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis.
Vitamin D that we obtain from sun exposure, foods, and supplements is actually not functional quite yet and must undergo two processes in the body for activation.
The first process (hydroxylation) occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as “calcidiol.”
The second hydroxylation occurs mainly in the kidney and forms the active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as “calcitriol.”
Vitamin D can then promote calcium absorption in the gut, maintain adequate serum calcium and phosphate concentrations to enable normal bone mineralization and to prevent cramps and spasms. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts. In addition vitamin D works with calcium to help protect older adults from osteoporosis.
Safety and Side Effects of Excessive Vitamin D Supplementation
When taken in appropriate amounts Vitamin D is generally considered safe. However, taking too much vitamin D (in the form of supplements) can be harmful. Children age 9 years and older, adults, and pregnant and breastfeeding women who take more than 4,000 IU a day of vitamin D might experience: nausea and vomiting, poor appetite, weight loss, constipation, weakness, heart problems, and kidney damage.
See this reference to the MayoClinic for possible medication interactions.
What happens if I am deficient in Vitamin D?
Without sufficient vitamin D, bones can become thin, brittle, or misshapen. This can lead to more fractures and broken bones. There are two major diseases related to a severe deficiency in Vitamin D, Rickets and Osteomalacia. Rickets is a disease of poor bone development due to inadequate calcium absorption. A popular symptom of this condition is bowed legs. Osteomalacia is a form of adult rickets where there is a loss of minerals in the bones and the bones become "spongy" and weak.
What are the next steps?
Get your Vitamin D blood levels checked.
If they are good, keep doing what you are doing! If not aim to find a vegan D3 supplement and some fortified foods.
Take your supplement and eat fortified foods regularly for a 3-6 months.
Get your levels checked again.
Mayo Foundation for Medical Education and Research. (2021, February 9). Vitamin D. Mayo Clinic. Retrieved December 31, 2021, from https://www.mayoclinic.org/drugs-supplements-vitamin-d/art- 20363792
Mangoo-Karim, R., Da Silva Abreu, J., Yanev, G. P., Perez, N. N., Stubbs, J. R., & Wetmore, J. B. (2015). Ergocalciferol versus Cholecalciferol for Nutritional Vitamin D Replacement in CKD. Nephron, 130(2), 99–104. https://doi.org/10.1159/000430813
U.S. Department of Health and Human Services. (n.d.). Office of dietary supplements - vitamin D. NIH Office of Dietary Supplements. Retrieved December 31, 2021, from https://ods.od.nih.gov/factsheets/vitamind-healthprofessional/
How much vitamin D do you need? Harvard Health. (2019, January 10). Retrieved December 31, 2021, from https://www.health.harvard.edu/staying-healthy/how-much-vitamin-d-do-you-need