Medically Reviewed by
Diana Morgan, MS, CISSN
4 min read
Vitamin D is essential for bone health and many of us simply don’t get enough of it. In fact, according to the US National Center for Health Statistics, over 70% of Americans get less than the daily recommended amount of vitamin D. While you can get vitamin D from your diet (think sardines, egg yolks, and cheese), the best source of vitamin D is from direct sunlight.
However, many people don’t get enough exposure to direct sunlight as they would need to meet their vitamin D needs. Regional factors like cloud cover patterns, smog, and the angle of the sun when it hits the earth can all impact how much sunlight exposure you are getting each day. In cities north of 37 degrees latitude (imagine a line drawn between San Francisco and Richmond, VA), it’s hard for people to produce enough vitamin D from sun exposure, especially between the months of November and March.
So how much do you need? The FDA recommends between 400 and 800 IU per day for children and adults through either your diet, exposure to the sun or supplementation.
Vitamin D is an essential nutrient and a fat-soluble vitamin. Best known for its role in supporting strong and healthy bones by helping to regulate calcium metabolism in your body, Vitamin D is also well researched for immune health. You can get Vitamin D through your diet in foods like sardines or salmon, egg yolks, cheese, and fortified milk. More commonly however, your body synthesizes vitamin D through moderate exposure to sunlight. If you don't get a lot of direct sun (e.g. exposed skin without sunscreen for at least 15 minutes daily), or if your diet is low in foods containing vitamin D, supplementing may be a good option.
Bone health: Most of us don’t start thinking about bone health unless we have a reason to, but strong joints and bones are essential at every stage of life. From before we’re even born to our older years, vitamin D plays a role in your evolving bone health. In utero, vitamin D helps support bone structure and tooth enamel development which is why it’s often found in prenatal supplements. As children and adults, vitamin D is necessary for calcium and phosphorus absorption, both major components of bone health.
Immune health: Vitamin D plays a critical role in supporting a healthy immune system and is one of the most well researched vitamins for immune health. Several placebo-controlled studies have shown that vitamin D can regulate the growth and function of immune cells, which are responsible for strengthening our bodies’ natural defense system. More specifically, vitamin D helps keep our immune system healthy by activating our T cells. T cells (AKA lymphocytes) form part of our adaptive immune system, constantly teaching it to recognize and react to antigen intruders. When T cells are exposed to an antigen (like foreign bacteria), they search for vitamin D to activate their immune response process.
How do you know if you might be deficient in vitamin D? The best way is to take a blood test and most doctors include Vitamin D screening as part of routine bloodwork You can request yourdoctor to give you a 25-hydroxy vitamin D test (AKA 25(OH)D test), or you can get a home kit to test your vitamin D levels at home. If you don’t get a lot of sun exposure, or don’t eat a lot of D-fortified foods or fish, you may want to consider taking a supplementThe signs of vitamin D insufficiency are often hard to see. Some may experience
These signs and symptoms are not specific to a vitamin D deficiency so if you’re experiencing any of them, make sure to talk to your doctors. Additionally, there are also several factors that may increase the likelihood of a vitamin D deficiency, like age, mobility, obesity, and certain diseases. If you’re at a higher risk for deficiency check with your doctor to get your levels tested.
You should speak with your doctor to determine the exact dose that is appropriate for you. Vitamin D used to be dosed in “international units” (i.e. IUs), but the FDA has updated their unit of measure to mcg. However, you may see both units of measure on labels. That National Academy of Medicine (the ones that make the Dietary Reference Intakes) recommend 15mcg (600 IU) of vitamin D for children and adults. The recommended dietary allowance may be higher if you are over the age of 70 (20 mcg). If you are deficient in Vitamin D, your doctor will likely recommend that you take a higher dose daily.
The severity of your vitamin D deficiency will determine how much vitamin D you need to take. Therefore, you will need to check your blood levels and talk with your doctor about how much vitamin D you should supplement with for your specific needs. For severe deficiencies, doctors will often order a prescriptiondose of vitamin D of 1250mcg (50,000 IU) to be taken once a week for several weeks For less severe or moderate deficiencies, physicians will often recommend consistent supplementation for 2–3 months at a predetermined dose.
There are no golden rules for when to take vitamin D supplements. However, there may be certain times that are better than others. There is some evidence that suggests vitamin D will be best absorbed when you take it with a meal that includes healthy fats (think avocados, fatty fish, and nuts) since vitamin D is a fat soluble vitamin.
Ultimately however, you should take vitamin D at a time of day when it is easiest for you to remember to take it. Many people prefer to take vitamins with breakfast as part of their morning routine to help them build a consistent habit.
When choosing a vitamin D supplement, look for a high quality product with transparent labeling so you know what you’re getting and where it comes from.
Vitamin D2 vs D3: There are two types of vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol). We suggest supplementing with vitamin D3, a naturally occurring and more bioavailable form of vitamin D, which means it will be easier for your body to digest and absorb.
Consider the source: Natural supplement forms of vitamin D3 come from two sources. Vegetarian D3 is most commonly derived from sheep lanolin and vegan D3 can be derived from algae. Both are effective sources so consider your own preference and sustainability practices when deciding between the two.