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Vitamin D Deficiency Facts

ccording to research published in the Journal of the American Osteopathic Association, nearly one billion people worldwide might have deficient (or at least insufficient) levels of vitamin D. Some are calling it an epidemic or pandemic, and most experts agree that modern life (including the widespread use of sunscreen) is at least partly to blame.


Contents of this article:


What is a Sufficient Amount of Vitamin D?

Vitamin D Deficiency Facts


Vitamin D is an essential nutrient for human growth and development. It is a fat-soluble, and works like a hormone that helps your body absorb calcium. You probably remember from your school days that it is important for strong bones and teeth. In the 1930s, the United States started fortifying some foods with vitamin D, which helped virtually eliminate rickets in children and osteomalacia in adults. But vitamin D is not naturally abundant in too many of the foods we eat, especially if you are averse to fatty fish or dairy products.


The Recommended Dietary Allowance (RDA) intake differs with age, but the following table shows the various recommendations. Note that these amounts are based on also receiving a minimal amount of sun exposure, and represent International Units per Day (IU/d).

Recommended Dietary Allowance (RDA) intake of Vitamin D


Data retrieved from National Research Council

** Data retrieved from Institute of Medicine (FNB)

*** Data retrieved from Endocrine Society


For those who are vitamin D deficient, many doctors recommend a loading dose of 500,000-600,000 IU (over a 2-to-3-month period) as treatment. People with blood serum vitamin D levels of less than 20 nanograms/milliliter (<20 ng/mL) are at risk for vitamin D deficiency. People with levels less than 12 nanograms/milliliter (<12 ng/mL) are deficient, require treatment and are probably experiencing symptoms. It’s important to note that levels greater than 50 nanograms/milliliter (>50 ng/mL, but more like >150 ng/mL) could lead to adverse effects.


The test to determine your vitamin D levels is called the “25-Hydroxyvitamin D” [25(OH)D] blood test, which you can purchase online as a home-testing kit or by visiting your doctor. But watch for these symptoms as potential indicators of insufficient vitamin D:


  • Cognitive difficulties (unclear thinking)
  • Brittle bones (easy fractures)
  • Soft bones (deformities over long term)
  • Bone pain
  • Muscle weakness
  • Unexplained fatigue or depression
  • Dry eyes


As you can see in the table above, some recommendations indicate that the appropriate amount of vitamin D could be higher than previously thought, especially for treating specific diseases like fibromyalgia and depression (although the evidence is not conclusive). But no adverse effects have been reported with regular supplemental vitamin D intakes of up to 10,000 IU/d.


Should I Let the Sunshine In?

Vitamin D from the Sun


Vitamin D is known as the “sunshine vitamin” which is a very appropriate nickname. The single largest source of our vitamin D is produced in our skin when exposed to the sun. On average, we get over 60% of our intake that way. The vitamin is not contained in the sun’s rays; rather, our bodies actually synthesize it in our skin using the sun’s ultraviolet-B (UVB) radiation. This might raise a question in your mind: “But what if I wear sunscreen?” Good question!


Sunscreens are designed to reduce the skin’s absorption of the sun’s ultraviolet radiation, which can cause sunburns and–after severe exposure–skin cancers. The synthesis of vitamin D is also reduced by these sunscreen products. The good news is that you are receiving some vitamin D while you’re outside, even when wearing sunscreen. The amount you are receiving depends on several factors, including:


  • The SPF factor of the sunscreen product (SPF 15 blocks 93% of UVB rays)
  • The way the product is applied (thin or thick with complete or partial coverage)
  • The activities you’re performing (swimming and perspiring can remove product)
  • The weather itself (sunny vs. overcast)
  • The time of day (high noon is strongest)
  • Where you live (no one above the 37th parallel receives enough UVB in winter)
  • Your own age and complexion (older and darker skin takes longer to react)
  • How long you’ve been wearing the product, and
  • How long you’ve been outside

For the average person wearing clothing that exposes the limbs, hands and face, it takes only about 15-20 minutes of bare-skin exposure (without sunscreen) at noon, to produce the recommended vitamin D intake. When you add the variables listed above, you can see that relying on sun exposure alone can be very inconsistent. Rather than trying to account for all of these variables, many doctors recommend taking vitamin D supplements just to be sure.


Should I Take a Vitamin D Supplement?

Should I Take Vitamin D Supplements


We can only get vitamin D in three ways: from sun exposure, by consuming certain foods and by taking vitamin D supplements. The U.S. government decided to fortify baby formula, whole milk, and breakfast cereals with vitamin D to help give our children a great start with bone health. But adults tend to not drink much milk (some are lactose intolerant). And according to a recent Swedish study, women are now being told that drinking the recommended three glasses of milk per day is not as healthy as we age, because it can cause an increase in mortality rates and bone fractures.


So, if you are dark-skinned or rarely exposed to the sun, and are not regularly eating fatty fish or drinking three glasses of milk per day, you might want to think about taking a vitamin D supplement. There are so many over-the-counter product options available, and many opportunities to find an appropriate amount as an additive to something else you already take. Multivitamins, calcium chews and fish-oil supplements are some great examples. Make sure to check the supplemental information on the labels of any products you are already taking to see how much vitamin D they contain.


In dietary supplements, vitamin D is found in two different forms: D2 (ergocalciferol) and D3(cholecalciferol). Both will increase the serum vitamin D levels in the blood, but vitamin D3seems to have a slight advantage over vitamin D2 supplements. Sunlight exposure produces vitamin D3 in humans and vitamin D2 in plants.


If you want to take vitamin D specifically for bone health, make sure you are also receiving enough calcium. High levels of vitamin D can be toxic. You should speak with your doctor if you believe you do have a vitamin D deficiency.



This article provides information that should not take the place of medical advice. You should talk with your healthcare providers (doctor, pharmacist, nutritionist) about your use of dietary supplements and what may be best for your overall health. Any mention in this article of a specific brand name is not an endorsement of the product.