This micronutrient is monumentally important for our bodies - especially our bones. But it's also the most commonly missed, with at least 8% of people in the United States and 1 billion people across the globe deficient in vitamin D. While it has many clear roles, scientists are still discovering the extent of other potential benefits vitamin D may contribute to our bodies (1).
This article takes you through why we need vitamin D, who has the highest risk of deficiencies, and how to make sure you're getting enough.
Vitamin D Benefits
While it has many significant influences, vitamin D is most well known for keeping our bones healthy and strong.
What Does Vitamin D Do?
1) Helps Calcium Absorption
Many people may have heard that calcium is critical for the growth and maintenance of bones, but fewer may be aware that vitamin D is needed for calcium to properly function. It does this by helping calcium to be absorbed from the intestines in order for it to be used throughout the body.
Calcium can’t function well without vitamin D. Effective absorption of calcium is not only important for proper bone growth and maintenance but also to prevent other dangerous consequences of low calcium.
2) Helps Bones Be Healthy & Strong
Supporting adequate calcium levels isn’t the only way this micronutrient helps our bone health.
Vitamin D also independently contributes to bone growth and a natural process of bone maintenance – called bone remodeling (2).
3) Immune System Support
While the details aren’t clear, vitamin D also seems to help our immune system. Low levels of the vitamin have been associated with an increased likelihood of infections and may also be associated with a higher number of autoimmune conditions.
While various claims have been made to it's potential relation to autoimmune conditions such as diabetes and multiple sclerosis, there isn't yet enough evidence to tell if there is a clear connection or influence between these conditions and vitamin levels (1, 3).
4) Cancer Influences
While there have been other claims that vitamin D may have a myriad of other benefits including impacting cancer risks, there is not enough evidence to make any conclusions on whether there is a true causative relationship between cancer and vitamin levels (2).
5) Inflammation Influences
There are also theories that vitamin D has anti-inflammatory effects on the body. However, the relationship between vitamin D and inflammation hasn’t been clarified. While some studies may show associations, we don’t have enough science yet to tell if it the vitamin exhibits true anti-inflammatory effects that may impact chronic diseases (4).
Vitamin D Deficiency
We do know that not enough vitamin D can lead to substantial negative consequences to our bones. The most significant of these skeletal effects are conditions called rickets and osteomalacia.
An estimated 8% of people in the United States meet criteria for deficiency and 17% have inadequate levels of vitamin D (5).
A deficiency of this vitamin can cause dangerous complications relating to low calcium.
Vitamin D Deficiency Causes
1. Limited Sunlight Exposure
2. Food Deficiency
Deficiencies can occur in three basic ways. Either your skin is not producing enough of the vitamin, you’re not getting enough supplementation in your diet, or you’re not able to absorb it from your intestines after you eat it.
Risk Factors for Vitamin D Deficiency
1) Breastfed Infants
There is often not enough vitamin D in breastmilk to support the needs of infants. This increases the risk of deficiency for exclusively breastfed infants. This risk can be reduced if the mother is careful about ensuring her levels are adequate as the content of vitamin D in breastmilk is probably directly related to the mothers own levels.
Because it is difficult to ensure that each mother's breastmilk contains enough of this vitamin, the American Academy of Pediatrics recommends that all exclusively breastfed infants be supplemented 400 IU daily (2).
2) Limited Sun Exposure
Sunlight exposure triggers our skin to make vitamin D. Therefore people who are not exposed to sunlight are at a greater risk for this deficiency if they aren’t careful about incorporating enough into their diet.
3) Dark Skin
People with darker skin produce less vitamin D in their skin with sunlight exposure than people with lighter skin. Therefore if they don’t have significant sunlight exposure and if they aren’t getting enough in their diet people with darker skin (more melanin) may be at higher risk for a deficiency.
4) Advanced Age
Older individuals are suspected to have a more difficult time producing vitamin D in their skin. They also in general may have a higher risk for not having a balanced diet that includes enough of the vitamin, and may also be more likely to not spend as much time outdoors.
5) Conditions Leading to Abnormal Intestinal Absorption
Conditions such as inflammatory bowel disease (IBD), celiac disease, and cystic fibrosis can all lead to abnormal absorption of vitamins that can lead to deficiencies. People who have a gastric bypass are also at risk for vitamin deficiency for a similar decreased ability to absorb nutrients (2).
Vitamin D Deficiency Symptoms
Most of the time people may not feel any symptoms, and likely do not know they have a vitamin deficiency unless they get a blood test. When symptoms do develop they are usually related to bone complaints as well as problems related to low calcium (hypocalcemia).
Osteomalacia describes ‘bone softening’ that is most commonly caused by vitamin D deficiency, but can also be caused by low calcium.
Symptoms of Osteomalacia
1) Fragile Bones
2) Joint Pain
3) Easily Broken Bones
4) Generalized Muscle Weakness
Rickets is the term for osteomalacia in infants and/or children. Bone growth is so important at these stages and becomes significantly disrupted in this disease.
Not only will these children develop weak bones, their bones will also grow abnormally.
Symptoms of Rickets
1) Stunted Growth
2) Bowed Legs
3) Bone Pain
4) Large Forehead
5) Easily Broken Bones
6) Abnormally Shaped Spine
Sources of Vitamin D
Vitamin D can be ingested through food or supplements, and can also be made by our skin when it is exposed to the sun. However it is not immediately in an active form when it enters the body. This means that our body needs to process it before it is able to be used.
1) Vitamin D Foods
Not that many foods contain vitamin D. To help people get all that they need the food and drug administration (FDA) adds it to commonly consumed food products.
Food products with specifically added nutrients are said to be ‘fortified’. Most of the vitamin D consumed by people in the United States comes from fortified foods.
Foods Commonly Fortified with Vitamin D
Food Sources Naturally Containing Vitamin D
2) Vitamin D Sun
With sun exposure, our bodies can make our own vitamin D. Sunlight acts as a catalyst to trigger a commonly found compound in the body (called 7-dehydrocholesterol) to turn into vitamin D.
Some specialists recommend sun exposure for at least 5-30 minutes twice weekly to help ensure adequate vitamin levels.
3) Vitamin D Supplements
While some people may feel it’s most ideal to get all of our vitamins naturally through food sources and sunlight, supplements can be very helpful in getting us what we need when important deficiencies are at stake.
Both vitamin D2 and vitamin D3 have been shown to be effective supplements, varying only slightly in their chemical structure.
D2 is also referred to as ‘pre-vitamin D’, or the more formal name is ergocalciferol. This is found in food sources from non-animal products as well as some supplements.
Vitamin D3 is also called cholecalciferol. It’s the same vitamin we have in our bodies. Food sources from animal products supply this vitamin as do some supplements.
Some people advocate for utilizing vitamin D3 as a supplement choice over vitamin D2 for the following reasons (5).
Proposed Reasons to Supplement D3 Instead of D2:
- Closest Match to Our Bodies Vitamin D
- Smaller Chance of Toxicity
- More Studied
- Longer Shelf Life
- Suspected to be More Effective
- Similar Price
Vitamin D Dosage
The Food and Nutrition Board developed the following recommended daily intake of vitamin D based on what would be adequate for at least 98% of healthy people (2). These suggestions are more formally called recommended dietary allowances (RDAs).
|Vitamin D Recommended Minimum Daily Intake|
|< 1 year||400 IU (10 mcg)|
|1-70 years||600 IU (15 mcg)|
|>70 years||800 IU (20 mcg)|
Because the sun can also influence vitamin D production, these recommendations were based on minimal sun exposure.
However, the FDA recommendations are up for debate, as other sources suspect these suggestions may be too low and that at least 1000 IU should be supplemented instead (1).
Vitamin D Levels
The blood test that is used to evaluate vitamin D levels is called 25-hydroxyvitamin D, abbreviated 25(OH)D.
Normal Vitamin D Level
Normal blood levels of 25(OH)D are thought to be >50mmol/L.
Low Vitamin D
Inadequate blood 25(OH)D is <50mmol/L. Severe deficiency is considered in levels <30 mmol/L.
Levels <30 mmol/L puts children at a high risk for developing major problems like rickets and places adults at a high risk of complications like osteomalacia.
Too Much Vitamin D
It seems there can always be too much of a good thing. Vitamin D levels that go way over recommendations can lead to some adverse effects. It’s thought that this toxicity can occur at blood levels of 25(OH)D > 500 mmol/L (2).
How much does this translate into what you take? While it’s suggested that vitamin supplementation of 4,000 IU should be the upper limit in one day, other sources have shown that up to 10,000 IU is safe.
Symptoms of Vitamin D Toxicity
1) Nausea & Vomiting
2) Decreased Appetitie
3) Heart Problems
4) High Calcium
It’s overall very hard to get levels this high and would only occur if there was a significant overdose in vitamin supplements. So you don’t need to worry about getting toxicity from eating too many vitamin D rich foods.
Because there are such limited sources of vitamin D, it’s critical to ensure that you’re including these options in your well-balanced diet, getting enough sun exposure, or taking supplements to otherwise meet all your micronutrient needs.