What is vitamin D?
Vitamin D is an essential nutrient known for its role in bone health. It’s also a unique nutrient because it’s both a fat-soluble vitamin found in your food and a hormone your body can make when your skin is exposed to sunlight. There are 2 primary forms of vitamin D: D2 and D3. Vitamin D2 (ergocalciferol) is found primarily in plants and fortified food products. Vitamin D3 (cholecalciferol) is found mostly in animals and is the form found in your skin. In addition to being essential for bone health, vitamin D plays several other roles in your body that could be important for military performance and mission readiness.
Why is vitamin D important for Service Members?
Your vitamin D levels could affect your physical and psychological health, performance, and mission readiness in several ways:
- Higher vitamin D levels are correlated with better performance on the Army Combat Fitness Test and improvement in other measures of physical fitness, such as power, strength, and aerobic endurance.
- Vitamin D deficiency is a risk factor for overuse injuries, such as stress fractures. Overuse injuries are the most commonly diagnosed injury in the military and can lead to reduced military performance and dropouts from training, exercises, or missions. Stress fractures, the type of injury most closely associated with Vitamin D deficiency, also result in substantial lost duty time and are very costly.
- Low vitamin D is also a risk factor for decreased immunity. Poor vitamin D status can increase your risk of illness, including common colds, the flu, and respiratory infections, potentially keeping you on the sidelines when you’re needed in action. Taking vitamin D supplements if your vitamin D levels are low can reduce the incidence, severity, and length of the infection, getting you back in the field sooner.
- Active-duty Service Members with a diagnosis of vitamin D deficiency are much more likely to have a diagnosis of depression than those with normal vitamin D levels. This relationship doesn’t mean vitamin D deficiency causes depression, but a relationship seems to exist.
You can find out your vitamin D status via a simple blood test. Your vitamin D levels may be reported in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L) depending on your lab. Vitamin D deficiency is when the vitamin D levels in your blood are too low for optimal health and performance. Global health experts often disagree about the cut-off points related to vitamin D status, so it’s important to follow the guidelines your healthcare providers have in place for your organization. But several health organizations fall in line with these Endocrine Society Clinical Practice Guidelines definitions:
- Vitamin D sufficiency: 30 ng/mL (75 nmol/L) or above
- Vitamin D insufficiency: between 21–29 ng/mL (52–72 nmol/L)
- Vitamin D deficiency: 20 ng/mL (50 nmol/L) or below
- Vitamin D toxicity: more than 150 ng/mL (374 nmol/L)
How do I get vitamin D?
An estimated 80–100% of your vitamin D comes from sun exposure. When you’re in the sun, ultraviolet B (UVB) radiation converts a chemical found in your skin into vitamin D3.
Vitamin D can also be found in foods. Foods with naturally occurring vitamin D are limited, but they include fatty fish, fish oils, egg yolks, butter, and liver. You can also get vitamin D from fortified foods. (Food fortification is the practice of adding vitamins or minerals to foods during processing to increase their nutritional value.) Foods fortified with vitamin D, such as milk, fruit juices, breads, and cereal, provide valuable sources of vitamin D and can help you reach your vitamin D needs.
Am I at risk for vitamin D deficiency?
An estimated 85% of the military population has low vitamin D levels. So understanding your risk factors and taking action if necessary could keep you from being part of this statistic. Risk factors for vitamin D deficiency include any factors that interfere with skin synthesis of vitamin D and limited intake of foods rich in vitamin D. Here are some of the risk factors:
- Having dark skin pigmentation can decrease the skin’s ability to make vitamin D from sun exposure. People with darker skin need to get more sun exposure than people with fair skin to produce enough vitamin D.
- Having excess body fat can decrease concentrations of vitamin D in the blood because vitamin D is a fat-soluble vitamin and can be absorbed and held within fatty tissue. As your BMI (body mass index) goes up, vitamin D levels typically go down.
- Where you live has a large impact on your risk for vitamin D deficiency. Living at high latitudes, further from the equator, limits your exposure to UV rays, and therefore, vitamin D production in your skin. In the United States, that line is at approximately 35 degrees north (along the same lines as Fayetteville, NC, or Albuquerque, NM). If you live above that line, sun exposure will contribute very little to your vitamin D levels during the cooler months. Also, if you live somewhere air pollution is regularly high enough to block sunlight and reduce UV exposure, that can also increase your risk for vitamin D deficiency.
- Limited exposure to the sun. Your risk for having low vitamin D levels can increase if you regularly use sunscreen or protective clothing, spend most of your day inside, or work at night.
- Aging decreases your skin’s ability to produce vitamin D from sun exposure. Service Members over age 30 have higher odds of vitamin D deficiency compared to younger Service Members. But it’s not clear whether this is due to the natural aging process, the frequent transition to supervisory roles (which are often indoors) through a Service Member’s career, or other factors.
- Having certain health conditions that affect the liver, kidneys, or gut can reduce vitamin D absorption and metabolism. So if you have an underlying medical condition that affects these organs, you could be at greater risk for vitamin D deficiency.
- Limited access to or intake of foods rich in vitamin D. Whether you live in a “food desert” where there aren’t many grocery stores, you’re deployed with less access to food variety, or you have a food allergy that keeps you from eating foods rich in vitamin D, you could be at greater risk for vitamin D deficiency.
Vitamin D deficiency risk assessment for military populations
Military life includes unique circumstances that put Service Members at risk for nutrient deficiencies. Check the graphic here to find out which risks for vitamin D deficiency might apply to you.
You can also download the Vitamin D Risk Assessment [PDF]
What can I do if I’m at risk for vitamin D deficiency?
Here are a few ways you can get more vitamin D:
- Eat fatty fish twice a week. Fish high in fat, such as trout and salmon, tend to have higher levels of naturally occuring vitamin D per 3-ounce serving compared to other types of fish.
- Choose milk or fruit juice, and cereal that’s fortified with vitamin D. Fortified foods are a great way to increase your intake of vitamin D. Various milk options are fortified with vitamin D, including plant milks, so be sure to check the labels.
- Eat the egg yolks. Some people toss their egg yolks because of the high calorie count. But egg yolks are loaded with various nutrients that are important for health, including vitamin D.
- Practice safe sun exposure. During the summer months in the continental United States (CONUS), as little as 15 minutes of sun exposure between 10 a.m. and 3 p.m., with your arms, legs, and face exposed, can be enough to meet your vitamin D needs. But given the various factors that can limit the effectiveness of vitamin D production in the skin and the increased risk of skin damage from sun exposure, taking vitamin D supplements may be the safest, most predictable way to increase your vitamin D levels.
- Talk to your doctor about taking vitamin D supplements. You might want to take vitamin D in winter when sun exposure is limited—or year-round, depending on your risk factors and baseline vitamin D status. Be sure to practice supplement safety if you and your medical provider decide taking supplements is right for you.
Understanding your risk factors for vitamin D deficiency can motivate you to take action. Having sufficient vitamin D levels can improve your physical performance, reduce your risk of fractures, and contribute to your overall physical and mental health—making you mission- and duty ready.