Why Vitamin D Is Important & How To Avoid A Deficiency

Oct 17, 2023 Immune SystemVitamin D 12 MIN

Why Vitamin D Is Important & How To Avoid A Deficiency

Many of us are already familiar with vitamin D, whether it’s from the colorful fortified orange juice bottles or that joyful feeling of relaxing in a ray of sunshine. Yet vitamin D is considered to be a “nutrient of public health concern” in the United States, because so many Americans have low vitamin D intakes, and low intakes are associated with health concerns.1 That’s because vitamin D benefits extend far beyond those few luxurious moments we spend synthesizing vitamin D3 in the sun. 

Low vitamin D intake is associated with many health risks, and yet data shows that 29% of the US population is vitamin D deficient and 41% are vitamin D insufficient.Not only that, but 95% of all adults in the US don’t get enough Vitamin D from their diet.3 Those are pretty high numbers considering the many important roles vitamin D plays in our overall health. Given vitamin D deficiencies are common, it’s worth noting which deficiency symptoms to look for, which foods contain vitamin D, how to choose the best vitamin D supplement, which personalized vitamins might be right for you, and what exactly should our vitamin D intake be if we’re going to get the most out of this vital nutrient. So, if you’re curious about the sunshine vitamin and are wondering “How much vitamin D should I take?” read on to have all your questions answered! 


Vitamin D is an essential, fat-soluble vitamin that plays many essential roles in the body. It’s vital to bone health and plays crucial roles in the immune and muscle systems as well.4

Vitamin D is essential for normal bone development and overall bone health

Vitamin D is probably best known for its role in normal bone development, maintenance, growth, and remodeling.4,5 Basically everything bone. We’re talking about your skeleton, here. Your teeth and all those bones that protect your heart, brain, and lungs.

Specifically, vitamin D helps the body both use and absorb calcium.6,7,4 If we aren’t consuming enough calcium, our bodies will steal it from our bones, eventually causing them to become smaller and weaker over time.8,6 Getting enough vitamin D is essential for making sure the body can absorb and use all the calcium we consume from our diets, and to supporting our overall bone health as we age.6,7,4

Read more about why your bone health matters now

Vitamin D plays a significant role in muscle health too

Vitamin D plays a significant role in muscle function as well. Vitamin D is needed for normal muscle development and in supporting  muscle strength and performance. One study on adolescent girls showed a positive association between vitamin D blood levels and muscle power, jump height, jump velocity, and force.9 In older adults, daily vitamin D supplementation at 800–1000 IU showed beneficial effects on both strength and balance.10 With such shortfalls of vitamin D, it’s no wonder we see symptoms such as kids lacking muscle power in sports, and older adults losing muscle mass.

Vitamin D plays two key roles in the immune system as well

Vitamin D plays a variety of roles in immune health. The immune system has two primary systems  (innate and adaptive) and vitamin D is critical to the optimal function of both.4


Vitamin D is a rare bird of a nutrient because it’s an essential nutrient the body can make on its own without solely relying on diet. But your body can only make it with sufficient sun exposure.

The best way to increase your vitamin D levels is from the sun

The best source of vitamin D is from at least 15 minutes of sunscreen-free sun exposure a few times a week. It’s best to get the sun between 10 AM and 3 PM and have your face, arms, legs, or back exposed. Factors such as season, latitude, cloud coverage, pollution, skin color, and age can affect the amount of time you need, so how often and amount of time you need in the sun can vary.5

There aren’t a lot of foods high in vitamin D

Few foods naturally contain vitamin D.5 Those that do, only offer small quantities of it, such as some fatty fish, eggs, and mushrooms depending on their vitamin D exposure from the sun.4 Fortified foods (such as milks, oatmeals, and juices) provide most of the vitamin D found in American diets.5

There’s a difference between vitamin D2 and vitamin D3

While figuring out how to increase your vitamin D, keep in mind that this nutrient comes in two forms: vitamin D2 and vitamin D3. Vitamin D3 is synthesized in skin in humans and animals from exposure to UVB rays.4 Vitamin D2 is found in plants (such as mushrooms) that are exposed to UVB rays.4 And if we consume those foods, we can gain a little bit of this nutrient for ourselves. Vitamin D2 and vitamin D3 are both used in fortified foods, juices, or milks.4

If you’re looking at supplementation, vitamin D3 is the preferred choice because it is more effective than vitamin D2 at raising and maintaining vitamin D blood levels.4


Now that you know the best way to get vitamin D is from the sun, you may be wondering “how much vitamin D should I take?” when calculating how much vitamin D you should be getting from diet or supplements. 

The daily vitamin D recommendations to support bone health are as follows:11

  • 600IU/daily for adults ages 19–71
  • 800IU/daily for adults ages 71 and over

The optimal vitamin D dose to cover all health benefits beyond bone, are:12

  • 1500–2000IU/daily for all adults

What’s the optimal intake for a dietary supplement?

Vitamin D is available in over-the-counter supplements and even personalized vitamin packs. In general, vitamin D supplements are safe and well-tolerated when following recommended guidelines. In terms of how much vitamin D per day, the recommendation for optimal supplementation is: 

  • 1500–2000IU/daily of Vitamin D3

Be sure to choose a high-quality supplement. While Vitamin D supplements can be taken at any time of day, be sure to take them with food for optimal absorption.

Can I get too much vitamin D?

If you are wondering, “how much vitamin D is too much?” you should know that it’s almost impossible to get too much vitamin D from the sun or natural food sources. When taking dietary supplements, it’s important to always follow recommendation guidelines and not go over recommended doses, or work with your health care provider when taking a high dose.13 If you have any symptoms of toxicity, such as headache, nausea, or vomiting, it’s important to see your health care provider and get your vitamin D blood levels checked. For people with kidney disease or hypercalcemia, it is recommended to check with health care provider before taking

Keep your medicines in mind when supplementing with vitamin D

Several medications can decrease vitamin D absorption in the intestine or may affect how vitamin D is metabolized.4 If you’re on several medications, it’s best to check in with your health care provider to make sure they are not affecting your vitamin D levels.


The most accurate way to measure your vitamin D levels is through a blood test. Most vitamin D in the blood is in a form called 25-hydroxy vitamin D (25(OH)D). This test is very commonly performed and is widely available. You can get the test from through your health care provider or local lab. When you get your test results back, look for these numbers:12

  • Deficiency: 25(OH)D <20 ng/mL (50 nmol/L)
  • Insufficiency: 25(OH)D ranging from 21 to 29 ng/mL (52–72 nmol/L)
  • Sufficiency: 25(OH)D > 30 ng/mL (75 nmol/L)
  • Toxicity: 25(OH)D > 150 ng/mL risk for toxicity

The sufficiency levels listed above are considered optimal ranges.

What are the symptoms of a vitamin D deficiency?

Symptoms of vitamin D deficiency or low vitamin D status are often vague and can be dismissed or attributed to everyday life annoyances. Symptoms include muscle aches and pains, muscle weakness, bone pain, fatigue, mood changes, not sleeping well, or even hair loss.4,14,15,16 Some people don’t notice any symptoms and are surprised when their doctor tells them their blood test came back showing a low vitamin D level. 

How do I treat a vitamin D deficiency?

Low levels of vitamin D are usually treated with a higher dose vitamin D supplement. The doses for vitamin D insufficiency can range from 2,000 to 10,000 IU, depending on the blood level. For a vitamin D deficiency, the Endocrine Society Practice Guidelines recommend all adults be treated with 50,000 IU vitamin D once a week for 8 weeks; or its equivalent of 6000 IU vitamin D daily to achieve a blood level of 25(OH)D above 30 ng/ml, followed by ongoing maintenance therapy of 1500–2000 IU/day. It’s important to work with your health care provider on the accurate dose to ensure you reach your optimum vitamin D blood levels.12

How long does it take to recover from a deficiency?

It may take a couple of months, but everyone is different. The course of therapy for vitamin D deficiency is approximately 8 weeks, at which point you should have your levels rechecked.  Some people may need to go a little longer. Hang in there.12

Vitamin D deficiency symptoms aren’t always obvious, but pay attention to your body, because low vitamin D may lead to health problems

We know almost 1/3 of the population has a vitamin D deficiency, and if not treated, this may lead to muscle loss, bone loss, and immune dysfunction. ,.4


Although nutrient deficiencies are usually related to a shortfall in diet, they can occur for a range of other reasons.5 Here are some of the key risk factors that could impact how much vitamin D your body needs, uses, or absorb—and therefore increase the risk of a vitamin D deficiency.

Your diet may put you at risk for a vitamin D deficiency

While the main source of vitamin D does come from the sun, diet still plays a major role in providing this critical nutrient. Diets that avoid key sources of vitamin D are associated with:5

  • Milk allergies
  • Lactose intolerance
  • Ovo-vegetarianism (excluding all animal-based products except for eggs)
  • Veganism

Location, air quality, cloud coverage, and seasons all affect your risk for vitamin D deficiency

Because sun exposure is our best source of vitamin D, environmental factors can affect how many of those vital UVB rays see the light of day.4 For example, if you live above certain latitudes or below at certain altitudes, your time in the sun may not yield as much vitamin D.4 Pollution and cloud coverage can drastically lower the intensity of the UVB rays that do reach your skin, while seasonal changes can affect the quantity and quality of those rays.4 All of these factors can affect how much vitamin D your body produces.4

Sunscreen and sun-protective clothing affect how much vitamin D you get

It’s important to protect our skin, but it’s also important to note that protecting our skin can also block the UVB rays it needs to produce vitamin D.4 Wearing hats, sunscreen, head coverings, or protective clothing can all inhibit our skin’s ability to soak up those rays, and hinder vitamin D production.4 Even applying something as light as 10 SPF sunscreen can reduce UVB radiation by as much as 90%!4

Having a dark complexion also increases your risk for vitamin D deficiency

Skin pigmentation can affect how much vitamin D your skin can make from sun exposure.4 People with a dark complexion make less vitamin D from exposure to sunlight than people with light-colored skin pigmentation.4

The older you are, the higher your risk is for a vitamin D deficiency

Growing older reduces the body’s ability to synthesize vitamin D from the sun.4 Older adults are also more likely to stay indoors, limiting their exposure to sunlight in the first place, and they’re more likely to use sunscreen.4

Chronic kidney disease can affect your risk of a vitamin D deficiency too

Vitamin D is synthesized in the skin, but it’s metabolized in the liver and kidney.4 Vitamin D deficiency in people with chronic kidney disease is due to reduced vitamin D synthesis and increased loss of vitamin D from urination.4

People with gastrointestinal diseases and fat malabsorption syndromes are at an increased risk for a vitamin D deficiency4

Vitamin D is a fat-soluble vitamin. Fat malabsorption syndromes, such as cystic fibrosis, and other conditions that affect intestinal absorption, such as Crohn’s disease, celiac disease, and inflammatory bowel disease are at risk of developing vitamin D deficiencies due to decreased absorption of this critical fat-soluble vitamin.4

Not getting enough magnesium may increase your risk of a vitamin D deficiency too

Magnesium is another essential nutrient, and it plays an important role in how the body metabolizes vitamin D.4 But magnesium is marked as an “under-consumed” nutrient in the American diet, with 45% of US adults not consuming enough of this mineral from their diets.3 Recent studies show, however, that increasing magnesium intakes reduces vitamin D insufficiency risks.4


After centuries of this vitamin being used for treatments, vitamin D is finally getting the attention it deserves when it comes to our health. Luckily, getting enough of this vitamin is often as simple as stepping outside to enjoy 15 minutes of sunscreen-free sun exposure or getting it through diet and supplements. No matter how we choose to increase our vitamin D intake, the important thing is that we’re now empowered with the knowledge this nutrient matters to our health and what to do about it.


This information is only for educational purposes and is not medical advice or intended as a recommendation of any specific products. Consult your health care provider for more information.


  1.  U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.
  2. Liu, X., A. Baylin, and P.D. Levy, Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr, 2018. 119(8): p. 928-936.
  3. Reider CA, Chung RY, Devarshi PP, Grant RW, Hazels Mitmesser S. Inadequacy of Immune Health Nutrients: Intakes in US Adults, the 2005-2016 NHANES. Nutrients. 2020;12(6):E1735. Published 2020 Jun 10. doi:10.3390/nu12061735 https://pubmed.ncbi.nlm.nih.gov/32531972/
  4. Oregon State University. “Vitamin D.” 2017. Linus Pauling Institute, Micronutrient Information Center. Accessed on: June 25, 2020. https://lpi.oregonstate.edu/mic/vitamins/vitamin-D
  5. US Department of Health and Human Services. “Vitamin D: Fact Sheet for Health Professionals.” 2020. National Institutes of Health Office of Dietary Supplements. Accessed on: June 25, 2020. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
  6. National Osteoporosis Foundation. “Calcium and Vitamin D are Essential for Bone Health.” Accessed on: June 25, 2020. https://cdn.nof.org/wp-content/uploads/2016/04/Calcium-and-Vitamin-D-are-Essential-for-Bone-Health.pdf
  7. Office of the Surgeon General (US). Bone Health and Osteoporosis: A Report of the Surgeon General. Rockville, MD: Office of the Surgeon General, 2004. https://www.ncbi.nlm.nih.gov/books/NBK45503/
  8. American Academy of Orthopaedic Surgeons. “Healthy Bones at Every Age.” 2012. OrthoInfo. Accessed on: June 25, 2020. https://orthoinfo.aaos.org/en/staying-healthy/healthy-bones-at-every-age/
  9. Ward KA, et al. Vitamin D status and muscle function in post-menarchal adolescent girls. J Clin Endocrinol Metab. 2009;94:559–563.
  10. Muir SW, et al. Effect of vitamin D supplementation on muscle strength, gait and balance in older adults: a systematic review and meta-analysis. J Am Geriatr Soc. 2011;59(12):2291‐2300.
  11. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  12. Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline.J Clin Endocrinol Metab. 2011;96(7):1911-1930. https://pubmed.ncbi.nlm.nih.gov/21646368/
  13. Dudenkov DV, et al. Changing Incidence of Serum 25-Hydroxyvitamin D Values Above 50 ng/mL: A 10-Year Population-Based Study. Mayo Clin Proc. 2015;90(5):577-586. https://pubmed.ncbi.nlm.nih.gov/25939935/
  14. Ikonte CJ, et al. Micronutrient Inadequacy in Short Sleep: Analysis of the NHANES 2005-2016. Nutrients. 2019;11(10):2335
  15. Ju SY, et al. Serum 25-hydroxyvitamin D levels and the risk of depression: a systematic review and meta-analysis. J Nutr Health Aging. 2013;17(5):447‐455. https://pubmed.ncbi.nlm.nih.gov/23636546/
  16. Almohanna HM, et al. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatol Ther (Heidelb). 2019;9(1):51-70.


Carroll Reider, MS

Scientist, Principal Science & Technology

Carroll is a nutrition scientist and communicator with over 25 years of experience as a clinician, researcher, and educator at major universities, medical centers, and nutrition industry settings. She is a passionate advocate of nutritional health and established the nutrition education and science platforms at Pharmavite. Carroll is an expert in personalized nutrition and has published several scientific papers on vitamin and mineral inadequacies and the impact on health and wellbeing. Prior to joining Pharmavite, Carroll taught nutrition at UCLA Medical School and Santa Monica College and was a chief clinical dietitian and researcher.

Read More