Are you getting enough vitamin D?
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 one of the most common nutrient deficiencies. Studies show that between 30-80% of people simply don’t get enough vitamin D.
Understanding Vitamin D
Vitamin D (calciferol) isn’t “active” in our bodies. To do it’s job, 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, which 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.
Vitamin D deficiency happens when someone has less than 30 nmol/L of 25(OH)D in the blood. The ideal range is from 50-125 nmol/L (20 ng/L). Less than 30 nmol/L is considered deficient and more than 125 is considered high.
Vitamin D deficiency 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 with the conversion of the “previtamin” D into the active form.
Those who are more likely to be deficient in vitamin D include:
- Older adults
- 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
- People who have undergone gastric bypass surgery
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. To get vitamin D from foods and supplements the Institute of Medicine (IOM) has identified a “Recommended Dietary Allowance” (RDA) of:
- 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 has many functions in the body but 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.
Vitamin D for 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 to ensure optimal levels of calcium in the blood. When it comes to calcium, the body always prioritizes the blood over the bones because the blood transports calcium around the body for critical functions. This is why it’s more important to maintain the calcium levels in the blood over levels in the bones.
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.
Vitamin D, the immune system, and inflammation
Vitamin D seems to have “anti-inflammatory” and “antioxidant” properties and studies have shown a link between low levels of vitamin D and immune-related conditions like atopic dermatitis and rheumatoid arthritis. Some studies in people with immune conditions (e.g. cystic fibrosis, multiple sclerosis, & obesity), show that supplementing with vitamin D reduces some inflammatory markers in the blood. Additionally, some researchers think vitamin D, due to its effects on the immune system, may also help with serious food allergies. A few small studies have shown 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, therefore, 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 and colitis, as well as people who have had gastric bypass surgery.
Also, a healthy vitamin D status seems to go hand-in-hand with a healthy gut. A link has been established between sub-optimal vitamin D, gut microbiome status, gut inflammation, and diseases of the gut like IBD and colon cancer.
Vitamin D and cancer
Higher levels of vitamin D are associated with lower risk for colon, prostate, and breast cancers. Laboratory analysis shows that cancer cells don’t seem to 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 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, and some studies also show a link between low vitamin D levels and increased risk of Alzheimer’s and Parkinson’s diseases.
Forms and sources of vitamin D
Vitamin D comes in two different forms: D2 and D3. Vitamin D2 (ergocalciferol) is the plant-based form, and vitamin D3 (cholecalciferol) is from animals. The plant-based D2 form is manufactured by exposing yeast to UV radiation. The animal-based D3 form is made from lanolin.
Sun exposure, foods, and supplements are the three main sources of vitamin D. Our skin contains “pre” vitamin D. When exposed to UV rays from the sun, this “previtamin” is converted into vitamin D (calciferol). It’s a known fact that vitamin D levels decline in people throughout the winter. The problem with sun exposure 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.
Vitamin D is not naturally found in very many foods and the best sources include fatty fish and fish liver oils. It 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 limited to some mushrooms that have been exposed to the sun. Because it’s naturally found in so few foods, it is common for certain foods to be fortified with vitamin D. Vitamin D is a fat-soluble vitamin, therefore its absorption is improved when taken at the same time as a fat-containing meal.
The blood levels of calcium can get too high when supplementing with too much vitamin D. This can lead to “calcification” which can damage blood vessels, the heart, and kidneys. This risk is generally when taking supplements and not so much from sun exposure or food intake. Always check with your health care professional and/or pharmacist if you’re taking medications, as vitamin D supplements can interact with certain drugs.
In conclusion, vitamin D is necessary for its’ many health-promoting roles in the body including bone health. It is also associated with a healthy immune system, digestive system, heart and mental health, blood sugar regulation, fertility, and resistance to cancer. Research shows that 30-80% of people simply don’t get enough vitamin D. We can get vitamin D from sun exposure, some foods, and supplements.
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