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.
It’s also the most common nutrient deficiency! Like most vitamins, vitamin D has many functions in the body. It’s mostly known for its ability to help build strong bones. 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.
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, calcidiol 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).
Since vitamin D is fat-soluble, any excess gets stored in the liver, and isn’t flushed out in the urine like water soluble vitamins. For example, you may have noticed your urine turning neon yellow after taking a B-complex. This is in response to excess riboflavin or B2, which is water soluble. The downside is, too much vitamin D (from excess supplementation) can become toxic in the body since the body doesn’t eliminate it. This is one reason it is very important to follow the recommended dose or the advice of a health care professional when taking supplements.
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 remodelling 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. The mineral calcium is one of the major players to “mineralize” and strengthen our bones.
FUN FACT: New research shows it’s not just the kidneys that activate 25(OH)D into 1,25(OH)D; bone cells can do this too!
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 calcium can then help to strengthen bones. 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 bone fractures.
Vitamin D, The Immune System, and Inflammation
Several studies have shown a link between low levels of vitamin D and immune-related conditions like atopic dermatitis and rheumatoid arthritis. In the lab, vitamin D seems to have “anti-inflammatory” and “antioxidant” properties.
FUN FACT: Inflammation is mostly caused by the response of our immune system.
Vitamin D can reduce immune response and inflammatory markers. Some studies in people with immune related health conditions such as cystic fibrosis and multiple sclerosis show that supplementing with vitamin D reduces some inflammatory markers in the blood.
Some researchers think vitamin D, due to its effects on the immune system, may also help with serious food allergies. A few small studies show that children with low vitamin D levels have an increased risk for food allergies.
Vitamin D and Digestive Diseases
Since vitamin D is fat-soluble, it’s absorbed along with fat in the diet. People who don’t eat or absorb enough fat are at risk of lower vitamin D levels. This can include people with many digestive issues such as celiac disease, inflammatory bowel diseases (IBD) like Crohn’s & colitis, as well as people who have had gallbladder or gastric bypass surgery.
Also, a healthy vitamin D status seems to go hand-in-hand with a healthy gut. For example, there is a link between sub-optimal vitamin D, gut microbiome status, gut inflammation, and diseases of the gut like IBD and colon cancer.
Vitamin D and Cancer
It’s not just colon cancer that’s associated with low levels of vitamin D. Higher levels of vitamin D are associated with lower risk for prostate, and breast cancers.
In the lab, cancer cells don’t do as well when exposed to higher levels of vitamin D. They don’t divide or invade other tissues as well; and, they seem to die easier.
Vitamin D and Heart Health
Several studies have linked low levels of vitamin D in the blood with heart disease.
Higher levels of vitamin D in the blood may reduce blood pressure and the risk of heart disease.
Vitamin D and Blood Sugar
Low vitamin D levels are associated with higher levels of insulin resistance in people without diabetes. It may also increase the risk of developing diabetes.
Supplementing with vitamin D may help improve blood sugar management in people with diabetes.
Vitamin D for Mental and Brain Health
Cells in key areas of the brain have “receptors” for vitamin D. Vitamin D also has a role in circadian rhythms and sleep, affects growth of nerve cells, and impacts the developing brain.
There is growing evidence of the links between low blood levels of 25(OH)D and symptoms of depression.
Some studies also show a link between low vitamin D levels and increased risk of Alzheimer’s and Parkinson’s diseases.
Vitamin D and Fertility
Vitamin D seems to help improve the motility and survival of sperm cells.
Both too high and too low levels of vitamin D in the blood seem to be associated with infertility.
Forms of Vitamin D
Many vitamins come in more than one form. With vitamin D, it comes in two different forms: D2 and D3. There are small differences in their chemical structure.
Vitamin D2 (ergocalciferol) is the plant-based form, while vitamin D3 (cholecalciferol) is from animals. At higher doses, however, vitamin D2 is less potent than vitamin D3 and I recommend supplementing with D3.
Sources of Vitamin D
There are three main sources of vitamin D – sun exposure, foods, and supplements.
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.
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.
Naturally occurring plant sources of vitamin D2 are some mushrooms that have been exposed to the sun and 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 Canada.
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.
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.
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 from sun exposure or food intake.
In infants, since formulas must have vitamin D added to them, breastfed infants are often recommended vitamin D drops. Speak with your licensed healthcare professional for recommendations.
Vitamin D Deficiency
Studies show that between 30-80% of people simply don’t get enough vitamin D. This deficiency is so common that some researchers have called it a “public health concern” and a “global problem.”
Vitamin D deficiency is considered having less than 30 nmol/L of 25(OH)D in the blood test. Ideally you want at least 50 nmol/L (20 ng/L).
<30 nmol/L = deficient
30-50 nmol/L = insufficient
50-125 nmol/L = adequate
125+ nmol/L = high
Vitamin D deficiencies can happen when, over time, people are not getting enough safe sun exposure, or are not eating enough foods containing vitamin D. It can also happen if the vitamin D is not being absorbed very well, or if the kidneys have trouble converting the “previtamin” D into the active form 1,25(OH)D.
People who are more likely to be deficient in vitamin D include:
Pregnant and lactating women, and breastfed infants;
People with limited sun exposure (including athletes who train indoors);
People with darker skin;
People with digestion issues that prevent proper absorption (e.g. inflammatory bowel disease, celiac disease, etc.);
People with obesity; and,
People who have undergone gastric bypass surgery.
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 15-30 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), is considered a minimum requirement. 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.
Vitamin D has many health-promoting roles in the body. Most of the evidence is for bone health, but it’s also associated with a healthy immune system, digestive system, heart and mental health, blood sugar regulation, fertility, and resistance to cancer.
Vitamin D is also the most common deficiency.
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 don’t have a test or professional recommendation, following the label directions on your vitamin D supplements can be a safe option to increase your vitamin D levels. When working with clients, I never recommend more than 4,000 IU/day unless blood work indicates a deficiency. Interested in supplementing with Vitamin D? Explore Peak Results Nutrition Online Dispensary for high quality professional grade supplements.
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