Vitamin D is vital to health; there are vitamin D receptors in almost every part of the body. It is involved in nervous system, cell growth, reducing inflammation and maintaining the calcium and phosphorus balance in the body.
Where does vitamin D come from?
Body: Our bodies make vitamin D by converting UV rays absorbed through the skin and then
distributing the hormone throughout the body(1).
Food: Vitamin D is primarily found in animal products, most abundantly in fish and eggs. A smaller amount, found in mushrooms is the only naturally occurring plant source as mushrooms are able to convert vitamin D in a similar way that humans do. Many commercial mushrooms are not grown under UV light and have much less than those grown naturally. Fortified foods such as dairy products, orange juice and cereals also have vitamin D3(2).
What does vitamin D do in the body?
Vitamin D is responsible for assisting with calcium absorption in the small intestine and helps the body maintain adequate serum calcium levels. Because of this, it’s necessary for bone growth and remodeling and helps prevent bones from becoming thin or brittle. A vitamin D deficiency in children results in rickets, and in adults is seen as osteomalacia and osteoporosis.
Not only a superstar bone supporter, vitamin D has been shown to help with immune function showing that those deficient in vitamin D are more susceptible to infection.2 The body uses vitamin D to make cholesterol, which is necessary for the production of hormones, building of tissue and creation of bile in the liver(3).
Who could be deficient in vitamin D?
Since most of us rely on the sun to get our vitamin D, those who don’t spend at least 15 minutes in the sun per day without sunscreen could be at risk. We always recommend using sunscreen before and during sun exposure.
The National Institutes of Health state that cloud cover can reduce UV energy by 50 percent and additional shade reduces it by 60 percent. Those with darker skin have more melanin present and therefore less able to product vitamin D from sunlight(4).
Those who do not eat fish or animal products are also a greater risk of being vitamin D deficient, especially if they consume a primarily whole foods diet, lacking in ‘enriched’ processed foods.
Older adults have a greater risk of vitamin D deficiency as they tend to spend more time indoors and are more likely to be susceptible to bone fractures.
Yes, vitamin D is known as the sunshine vitamin because our skin can produce it during the right conditions when we are in the sun.
Living in the northern hemisphere, sunscreen, wearing clothing that block the UVB rays can make it challenging to generate enough vitamin D from the sun.
In fact the actual amount of sun time a person needs in order to generate vitamin d varies depending on age and skin tone-the darker your skin tone the more sun time you need. On average most people would get adequate vitamin D during the summer if they were outside between 10-30min 2-4 times per week(5).
You might be thinking, well if there is no sun then I will just eat my way to adequate vitamin D.
I would love to do that too, but that could prove to be challenging. Look at this list of some common foods and the amount you would need to eat in order to meet the Recommended Daily Intake of 600IU (international units) is: 14 eggs, 15-7 ounce servings of pork, 10-5 ounce cans of tuna fish, 86-1 cup servings of (un-sunned) whole button mushrooms.
Eating salmon or sunned mushrooms everyday is your only option.
According to the USDA database: 1-4oz serving of salmon or 1.5 cups of (sunned) whole button mushrooms would provide the recommended 600 IU’s.
Should I supplement and if so, what kind D2 or D3?
Ultimately, if you do not eat very specific foods, live in the southern hemisphere and go outside 2-4 times per week, then add a dietary supplement to our diet. The most bioactive form is D3, and that comes a variety of animal sources. The D2 form comes from UVB exposed mushrooms and is vegan. (6)
Is there such a thing, as too much vitamin D? Yes, play it safe and take less than the tolerable upper limit unless a doctor recommends more. (7)
Tolerable upper intake level has been set at 4,000IU for children over 9y and adults. Toxicity has been documented with intake of 10,000IU+ per day in as little as 3 months. Symptoms are not always obvious and take time to manifest. Worst case scenario is kidney problems, hyper calcemia and calcification of soft tissue.
- The physiology of vitamin D. Vitamin D Council. https://www.vitamindcouncil.org/the-physiology-of-vitamin-d/. Published July 6, 2016. Accessed September 7, 2018.
- Appendix 12. Food Sources of Vitamin D. Chapter 4 – 2008 Physical Activity Guidelines.
- Vitamin D and Health. Obesity Prevention Source. https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/vitamins/vitamin-d/#vitamin-d-sources-and-function. Published March 15, 2018. Accessed September 7, 2018
- L.D. KZRD. Vitamin D toxicity: What if you get too much? Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108. Published February 7, 2018. Accessed September 7, 2018.
- Publications, H. H. (n.d.). Time for more vitamin D. Retrieved June 22, 2017, from https://www.health.harvard.edu/staying-healthy/time-for-more-vitamin-d
- For health professionals: Council position statement on supplementation, blood levels and sun exposure. (n.d.). Retrieved June 22, 2017, from https://www.vitamindcouncil.org/for-health-professionals-position-statement-on-supplementation-blood-levels-and-sun-exposure/
- How do I get the vitamin D my body needs? (n.d.). Retrieved June 22, 2017, from https://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get-the-vitamin-d-my-body-needs/