According to this study, a whopping 36% of healthy adults and up to 57% of general medicine inpatients in the U.S. dont get enough vitamin D.
Vitamin D Deficiency Risk Factors
Factor 1: Low sun exposure
Vitamin D is made in the skin through sun exposure. This relationship between sun exposure and bone strength was first observed by the ancient Greek historian Herodotus in 525 BC. He noted that the skulls of Egyptians (who had ample sun exposure) were far stronger than those of Persians (who covered themselves). Now, of course, we have more than a mere correlation.
If you’re curious, here’s how we now know the sunlight -> vitamin D process works:
Cells in your skin already have a precursor (called 7-dehydrocholesterol) that sunlight converts into previtamin D3. The vitamin D3 then leaves your cells and enters your circulatory system, bound to a protein (vitamin D binding protein, DBP). There it floats around until it is stored in fat cells or turned into another form (called 25-hydroxyvitamin D). Next, it goes to the kidneys for conversion to the active hormonal form (calcitriol), where it can start to help out various body systems.
Geographic location is critical to overall sun exposure because it determines how much sun you can get in a day. If you live in a climate that has a very cold winter, going outside with exposed skin isn’t really an option. The shorter days in colder climates definitely don’t help.
Low sun exposure can also occur if you don’t go outside enough, period. Or, if you tend to consistently slather on high SPF sunscreen.
Factor 2: Low Vitamin D in the diet
Unfortunately, vitamin D is difficult to get from food alone.
- Found in: Fatty fish like cod, salmon, and tuna. Mushrooms, egg yokes, and fortified cereals, juices, and dairy products (see NIH list here). And, of course, in vitamin D supplements.
Other factors that contribute to your personal risk of vitamin D deficiency:
- Skin color (darker shades require longer sun exposure for vitamin D synthesis)
- Age (the older you get, the less of the precursor called 7-dehydrocholesterol exists in your skin to be converted)
- Pollution exposure (higher pollution = less vitamin D synthesis)
- Sunscreen use (strictly blocking UV also blocks synthesis)
Why Does Vitamin D Matter?
Vitamin D deficiency is problematic because the so-called “sunshine vitamin” plays important roles in immune, bone, and skin health.
- Immune: Many of the cells that make up the immune system respond to vitamin D, making vitamin D an “immune modulator”. As a result, people with vitamin D deficiency are more susceptible to infection.
- Bone: Vitamin D deficiency results in decreased calcium absorption, and is associated with bone demineralization.
- Skin & Hair: Vitamin D’s active form plays important roles in building your skin’s barrier, protecting against hair loss, and even reducing your risk of cancer.
Five symptoms of Vitamin D deficiency
1) Poor healing or frequently getting sick
Vitamin D is necessary for optimal immune function, and therefore deficiency can lead to both wounds and sicknesses hanging around for longer. This study (of 19,000 people) found that people with low vitamin D were more likely to suffer from the common cold.
2) Fatigue
This study showed that in patients who suffered from fatigue, 77% were deficient. Their fatigue symptoms were significantly improved through vitamin D therapy.
3) Bone-related pain, mass loss, or fractures
According to this study, low vitamin D prematurely ages bones, leading to a 22-31% increase in the start and spread of fractures.
4) Depression and/or low mood
Though more research is necessary, some individuals with depression (or seasonal affective disorder) experience an improvement in symptoms following vitamin D increase (either through supplementation or light therapy). Review here.
5) Muscle pain or strong muscle soreness that is slow to improve
Pain-sensing nerves (in rats and humans) actually have vitamin D receptors. As a result, this study in rats showed that muscle pain could be brought on by vitamin D deficiency. Individuals suffering from chronic pain and conditions like fibromyalgia can sometimes find some relief from supplementing vitamin D.
Unfortunately, these symptoms are all very general, so the only sure-fire way to find out if you’re vitamin D deficient is to do a blood test. The blood test will look at your levels of a particular vitamin D precursor (25-hydroxyvitamin D) that’s easy to find and measure.
You can always try supplementing it, getting more sun, or eating more vitamin D-rich foods. Keep track of any changes to your symptoms.