Vitamin D - Are You Getting Enough?
Are You Getting Enough Vitamin D For your bones?
Vitamin D is an essential fat-soluble vitamin. It’s sometimes called the “sunshine vitamin” because our skin makes it when exposed to the sun. In the winter, especially in Canada we are not exposed to the sun as much so it is harder for our bodies to make the required amount of vitamin D we need.
Like most vitamins, vitamin D has many functions in the body. It’s mostly known for its ability to help build strong bones. But, vitamin D is also important for a healthy immune system, digestive system, heart and mental health, blood sugar regulation, fertility, and resistance to cancer.
FUN FACT: Vitamin D is the vitamin with more scientific articles published since 2000 than any other vitamin.
Let’s talk about the many roles vitamin D has in promoting good health. We’ll first go over what vitamin D does in our body (bones) then I will go over the different forms of vitamin D. Finally, I’ll give you three sources of this critical nutrient and how much we should get.
Make sure you’re getting enough!
Vitamin D in the body
Vitamin D (calciferol) isn’t “active” in our bodies. To do its wonders, it first needs to be converted into the active form. This is a two-step process. First the liver converts it into 25(OH)D (calcidiol). Then, that is converted into 1,25(OH)D (calcitriol) in the kidneys. It’s this third, calcitriol, form that’s active in the body.
Vitamin D acts like a hormone! That means it’s produced in one part of the body (e.g. the skin), and travels through to act on another part (e.g. the bones).
Because vitamin D is fat-soluble, when you have more than enough, it gets stored in the liver, and isn’t flushed out in the urine like excesses of many other vitamins are.
FUN FACT: Fish liver oil contains vitamin D, but not fish oil - it’s the liver that stores vitamin D.
Vitamin D for bones
Vitamin D is most known for its importance for bone health. Bones are alive and are constantly remodeling themselves. This means they, as all tissues, need a constant supply of nutrients.
How does vitamin D help your bones?
Vitamin D helps the body absorb calcium more efficiently. And the mineral calcium is one of the major players to “mineralize” and strengthen our bones.
Vitamin D works with other hormones to ensure optimal levels of calcium in the blood. When it comes to calcium, the body always prioritizes the blood over the bones. This is because the blood transports calcium around the body for critical functions like contractions of the heart and muscles. This is why it’s more important to maintain the calcium levels in the blood over levels in the bone.
When there is enough calcium in the blood, any excess is stored in the bones. This is when the bones are mineralized and strengthened. When there isn’t enough calcium in the blood two things happen to raise this level. First, vitamin D stored in the liver is activated to help absorb more calcium from food. Second, the body removes calcium stored in the bones to raise levels in the blood.
When we don’t get enough vitamin D (and calcium) regularly, bones can become weak and brittle. In children, severe vitamin D deficiency can cause rickets, and in adults it can cause osteomalacia. With less severe vitamin D (and/or calcium) “insufficiency” (as opposed to a more severe “deficiency”), osteoporosis can develop over the long term.
Having enough 25(OH)D in the blood is associated with higher bone density. Studies show that supplementing with vitamin D may reduce the risk of falls and bone fractures.
Sources of vitamin D
There are three main sources of vitamin D - sun exposure, foods, and supplements.
Sources of vitamin D - Sun exposure
Our skin contains “pre” vitamin D. When exposed to UV rays from the sun, this “previtamin” is converted into vitamin D (calciferol).
In fact, vitamin D levels decline in people throughout the winter.
The problem is that too much UV radiation can contribute not only to skin cancer, but also to dryness and other cosmetic changes in the skin over time.
Let’s look at how to get enough vitamin D from foods and supplements.
Sources of vitamin D - Foods
Vitamin D is not naturally found in very many foods. The best sources include fatty fish and fish liver oils. Some is also found in beef liver, some cheeses, and egg yolks. Because these are animal sources, they are in the D3 form. Some is even already converted into 25(OH)D which is thought to be 5 times more potent than the regular D3 form.
Naturally occurring plant sources of vitamin D2 are some mushrooms that have been exposed to the sun. That’s about it.
Because it’s naturally found in so few foods, vitamin D is also added to certain foods. This is called “fortification.” In fact, fortified foods are the main source of dietary vitamin D in the US.
Fortification of food with vitamin D can improve vitamin D status.
Some of these vitamin D fortified foods include milk, some orange juices, breakfast cereals, and yogurt. Check your labels to find out if yours has been fortified with vitamin D (it will be listed as an ingredient). You can also check which form of vitamin D was added: D2 or D3.
Infant formulas in Canada and the US are required to have at least 40 IU of vitamin D for each 100 kcal.
FUN FACT: Because vitamin D is a fat-soluble vitamin, absorption from foods, drinks, and supplements is improved when taken at the same time as a fat-containing meal.
Sources of vitamin D - Supplements
Vitamin D supplements come in both forms: D2 and D3. The plant-based D2 form is manufactured by exposing yeast to UV radiation. The animal-based D3 form is made from lanolin.
If you are at risk for vitamin D deficiency, your health care provider can test your blood for levels of 25(OH)D and recommend a course of action specific for you.
However, if you don’t have a professional recommendation for how much vitamin D to take, the safest way to supplement is to follow the instructions on the label. And never take more than 4,000IU/day (100 mcg/day), unless told to by your licensed health care provider.
That’s because too much vitamin D can become toxic. One effect of too much vitamin D is that blood levels of calcium can get too high. This can lead to “calcification” which can damage blood vessels, the heart, and kidneys. Getting too much vitamin D is mostly a risk when taking supplements; not so much from sun exposure or food intake.
And don’t forget to check with your doctor and/or pharmacist if you’re taking medications because vitamin D supplements can interact with some of them.
How much vitamin D do we need?
For adequate blood levels of 25(OH)D, how much vitamin D do we need to get every day?
To get enough vitamin D from the sun, a general rule is to get about 5–30 minutes of sun between 10:00 a.m. & 3:00 p.m. at least twice a week to the face, arms, legs, or back without sunscreen.
When it comes to vitamin D from foods and supplements, in Canada and the US, the Institute of Medicine (IOM) has set target daily amounts. This amount, called the “Recommended Dietary Allowance” (RDA), ensures that at least 97% of people get enough vitamin D every day. Those recommendations are:
- 10 mcg (400 IU) per day for infants under the age of one.
- 15 mcg (600 IU) per day for everyone aged 1-70 years old, including pregnant and lactating women.
- 20 mcg (800 IU) per day for everyone over the age of 70.
Vitamin D in foods and supplements may be measured in both mcg (micrograms) and/or IU (international units). The conversion factor is 40 IU = 1 mcg.
We can get vitamin D from sun exposure, some foods, and supplements.
The best way to know how much vitamin D you need is to have your blood tested if you’re at risk. If you don’t have a test or professional recommendation, following the label directions on your vitamin D supplements can be a safe way to get enough.