Vitamin D is actually a hormone in the body. Its main role is to regulate calcium in the blood to help maintain bone health. That means it’s important to keep bones and teeth healthy, but it does a ton more as well – we’ll get to that in a moment!
Vitamin D is produced when sunlight hits your skin, by a reaction between a compound called 7-dehydrocholesterol (found in your skin) with the sun’s ultraviolet light.
We can also get vitamin D naturally through food and via supplements.
Adequate blood levels are important to maintain bone and overall health. The information below shows blood levels for deficiency and adequacy:
Vitamin D Deficiency: <30 nmol/L, <12 ng/L
Inadequate for bone and overall health: 30 to <50 nmol/L, 12 to <20 ng/L
Adequate for bone health: >50 nmol/L, >20 ng/L
High level, linked to potential adverse effects: >125 nmol/L, >50 ng/L
First and foremost, vitamin D is essential to bone health. It’s important for absorption of calcium and mineralization of bone, which means it helps with improving bone mineral density. Adequate vitamin D can decrease fracture risk, especially in older adults. This is because vitamin D deficiency is associated with both muscular weakness and low bone mineral density.
But adequate vitamin D levels are important to people of all ages, especially teens and younger adults who are at an age where they are building, optimizing, and seeking to maintain bone mineral density. Vitamin D deficiency is linked to a bone disease called rickets that is mostly seen in children and is very rare now in the US, thanks to a successful government campaign to eradicate it, which has supplemented staple foods like milk with added Vit D since the 1930s.
Vitamin D is also a major player in muscle health and strength. Vitamin D receptors have been found in muscle tissues, and vitamin D blood levels between 40-90 nmol/L are associated with better muscle strength then individuals with blood levels <40 nmol/L. Falls in older adults are associated with muscle weakness and lower vitamin D levels, but supplementing vitamin D in older adults can help decrease risk of falls and fractures, too.
Vitamin D receptors have also been found on immune cells, and vitamin D has been shown to enhance the activity of immune cells. Maintaining adequate vitamin D levels also plays a role in taming inflammation, and evidence suggests it may decrease some inflammatory markers.
Studies have shown that vitamin D supplementation during pregnancy can help decrease the risk of preeclampsia, gestational diabetes, small for gestational age infants and overall supports fetal growth.
Now that you’ve got a sense of the important roles vitamin D plays in our daily life, you’re probably wondering how you can ensure you’re getting enough!
Vitamin D is primarily synthesized from the sun's UV rays, specifically UVB rays. There are UVA and UVB sun rays, and not every part of the world gets UVB rays year round. UVB rays are only available in the northern hemisphere April-September; we recommend checking with local public health guidance or consulting your doctor before starting a course of supplements.
Maximal production of Vitamin D occurs at exposure to UVB rays for 10-15 minutes in the summer months. Even if UVB is available, if you aren’t out getting enough sunlight, you may not be creating enough vitamin D, and other factors, such as melanin levels in your skin also affect UVB absorption. Those with darker skin need more sun exposure to get the same Vitamin D benefit as those with lighter skin. (It’s believed that at any given point, up to half of the world’s population may not get enough sunlight to produce adequate vitamin D levels, and 40% of US residents are deficient in vitamin D.)
There are two main types of vitamin D you may find in supplements: vitamin D2 and vitamin D3. Vitamin D2 is mostly “man made” and found in fortified foods and vitamin D3 is synthesized from the sun and also found in animal based foods (6).
Here are some foods high in vitamin D you might already incorporate into your diet!
Salmon is a tasty fatty fish and is among the best vitamin D foods. Per the USDA, a 3.5oz serving of farm-raised Atlantic salmon packs 66% of your DV of vitamin D – 526 IU. However wild-caught salmon contains even more vitamin D.
Because of its versatility – it can be eaten raw, canned, smoked, pickled, or cooked in any number of ways – herring is enjoyed around the world. It’s also a great source of vitamin D – a 3.5oz serving of the small fish contains 27% of your DV.
Another fish commonly enjoyed from a can, tuna, is another economical option when it comes to getting vitamin D from fish. 3.5oz of canned tuna contains 34% of your DV! It’s also a great source of niacin and vitamin K. Just be careful not to overdo it – like most fish, tuna contains trace amounts of methylmercury which can build up in your body and cause health issues.
Another canned fish that’s a great source of vitamin D is sardines. Your standard can of 3.8oz of the little salty fishes provides you with 22% of your DV.
This has been a decidedly fishy blog post thus far, so let’s pivot a bit over to the humble egg – seafood isn’t the only dietary source of vitamin D! The yolk isn’t always the most celebrated part of the egg – most of its protein is found in the egg white – but it is home to most of the fat, vitamins, and minerals. An egg yolk on average contains 5% of your DV of vitamin D, but that percentage will vary based on the sun exposure of the chicken that laid it; eggs from pasture-raised chickens will have a higher vitamin D count.
Among vegetables high in vitamin D, mushrooms reign supreme. Not counting foods fortified with the vitamin, mushrooms are pretty much the sole plant-based source of vitamin D available to us. Interestingly enough, much like humans, mushrooms possess the ability to synthesize this vitamin when exposed to UV light. And they do a good job of it. Certain varieties of wild mushrooms can pack up to three times your DV of vitamin D in a 3.5oz serving!
Because so few foods naturally contain vitamin D, especially if you adhere to a more plant-based diet, it’s good to know that there are plenty of options out there that have been fortified with this nutrient. If present, vitamin D will be touted on the nutrition facts for store-bought products, like cow’s or plant milks, both of which are typically fortified with vitamin D.
For supplementation, there are two forms: vitamin D2 and vitamin D3. Both are well absorbed in the body in the small intestine. Since vitamin D is a fat soluble vitamin, it is absorbed better with fat in the gut, though it is not necessary. The combination of Vitamin D3 with K2 can help increase its absorption and has shown to increase bone mineral density at greater levels.