What Everyone Should Know About Vitamin D

Written By Courtney Schmidt

When you think of Vitamin D, you likely also think of calcium and bone health. Why? Because Calcium and Vitamin D have long been recommended for healthy bones and prevention of osteoporosis and fractures—especially for women. Vitamin D also is a key factor in preventing rickets- a childhood disease that causes bones to soften, become deformed, and break.

But, is Vitamin D important for reasons beyond bone health?

Yes! There is more and more evidence pointing to Vitamin D’s role in other areas of health. And this is very important in determining whether a Vitamin D supplement would be beneficial and what dose you should take. 

In addition to helping create strong, healthy bones and prevent osteoporosis, Vitamin D (along with calcium) helps prevent fractures in older adults. 

Vitamin D is also now known to play a role in:

  • Reducing inflammation

  • Modulating cellular growth

  • Glucose regulation

  • Supporting metabolic processes

  • Prenatal and infant health

Vitamin D supplementation has been associated with:

  • Reducing metastatic cancer risk

  • Reducing risk of death from cancer

  • Lower risk of autoimmune diseases

  • Protection against bacterial lung infections

  • Preventing development of diabetes in pre-diabetics

  • Slightly lower risk of death from any cause in older adults

  • Supporting healthy pregnancies by lowering the risk of preeclampsia, intra-uterine mortality,

    preterm birth, small-for-gestational-age birth, and neonatal mortality

  • Contributing to cardiovascular health

What’s the controversy around Vitamin D supplementation?

In 2024, clinical practice guidelines for Vitamin D supplementation were updated by the Endocrine Society, and the group stopped short of recommending large-scale changes to the decades-old recommendations—who should be tested for vitamin D deficiency, who should take vitamin D supplements, what dose they should take, and what levels of vitamin D in the body are optimal for health. 

What is agreed upon:

It’s widely accepted that the following groups of people need Vitamin D supplementation in addition to the food and sunshine they consume daily: 

  • Children and adolescents 1-18 years of age

  • Pregnant women

  • Older adults above 75 years of age

  • High-risk prediabetics

Where disagreement occurs:

Although the Endocrine Society acknowledges current research demonstrating Vitamin D’s role in preventing cancer, lowering risk of death from cancer, maintaining lung health, reducing development of diabetes, and improving cardiovascular health, the expert panel stops short of recommending routine testing of Vitamin D levels in healthy children and adults (1).

The reason? Not enough clinical trial evidence available. 


How much Vitamin D should we consume? Same answer from the expert group. Not enough clinical trial evidence available. 

What levels of Vitamin D in our body are optimal for health? You guessed it. Not enough clinical trial evidence available so they decided to keep the recommendations as they’ve been since last updated nearly 30 years ago. 

The recommended daily allowance (RDA) of Vitamin D was initially based in 1941 on the amount of cod liver oil it took to prevent rickets and osteomalacia in children (400mcg). According to nutrition experts, the remarkably low recommended daily values for adults in the U.S. and Canada “illustrates that determination of vitamin D requirements and status has been more conjecture than science.” (2) 

Furthermore, “since publication of the 1997 recommendations for vitamin D, much has been learned regarding the metabolism of vitamin D. Thus, a major problem is that the [daily recommended intake] values are out of date with respect to recent evidence. 

Indeed, there is now sufficient information to set [recommendations] that more accurately reflect the data.” 

Here’s our take on Vitamin D Supplementation

If Vitamin D were not a vitamin but instead a patentable, proprietary drug product, there would be plenty of randomized, placebo-controlled clinical trials to determine the benefits, dose, efficacy, and monitoring parameters—paid for by a large pharmaceutical company that could earn millions from its success in the marketplace. 

Since a naturally-occurring vitamin doesn’t offer the same potential for financial windfall, the data is harder to come by. That leaves us with two choices—take a passive approach and wait indefinitely until enough data surfaces to comfortably make a recommendation OR take a hard look at the data we do have and make our best recommendation. 

Here’s our recommendation: 

  • Get baseline Vitamin D levels

  • Take oral Vitamin D3 (cholecalciferol) daily

  • Check Vitamin D levels in 6 months

  • Adjust dose as needed for optimal levels of 50-80 nmol/L

Scientific research demonstrates Vitamin D is not only necessary in lower doses to prevent rickets and osteoporosis, but likely helpful in higher doses in fighting off cancer, cardiovascular disease, autoimmune disease, lung infections, and diabetes. With such a massive potential upside and virtually no downside, this seems like a no-brainer.

For most people, daily oral Vitamin D3 (cholecalciferol) in the form of a supplement is ideal. Increasing Vitamin D-rich foods and time in sunshine also provide Vitamin D. However, sunshine can change with the season and comes with its own downside (UV exposure), and it’s difficult to get a ton of Vitamin D from food. 

There are risks if you take too much Vitamin D, so you should receive a lab test to verify your levels are in the optimal range. 


At your next annual check-up with your doctor, ask to add Vitamin D 25(OHD) levels to your blood work. You’re already getting blood drawn—it’s so simple! 

While Vitamin D 25(OHD) levels less than 30 nmol/L are considered deficient, international studies indicate higher blood levels of at least 50-80 nmol/L are optimal.2 

LEARN MORE

How Do We Get Vitamin D?

There are three main sources:

  • Sunlight: When your skin is exposed to UVB rays, your body makes vitamin D. Just 5–30 minutes several times a week on your arms, legs, or back (without sunscreen) is enough for most people (but always be sun safe).

  • Foods: Few foods naturally contain vitamin D. Good sources include fatty fish (salmon, trout), fish liver oil, egg yolks, and fortified foods like milk, breakfast cereals, and some plant milks.

  • Supplements: Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) supplements are widely available. Both can raise your vitamin D levels, but D3 is often more effective and longer lasting.

Who Is at Risk for Low Vitamin D?

Some people are more likely to have low vitamin D:

  • Babies who are exclusively breastfed.

  • Older adults (skin makes less vitamin D with age).

  • People with darker skin (more melanin reduces vitamin D production from sun)

  • People who spend most time indoors or cover their skin.

  • Those with certain health conditions (digestive disorders, obesity).

  • Individuals who avoid animal foods (since most dietary vitamin D is from animals)


Symptoms and Risks of Deficiency

Low vitamin D can lead to:

  • Weak bones and fractures

  • Muscle weakness

  • Fatigue

  • Increased risk of certain infections

  • In children, severe deficiency can cause rickets.


Are There Risks to Taking Too Much?

Yes—too much vitamin D, usually from supplements, can lead to toxicity (hypervitaminosis D).

Signs of too much include:

  • Nausea, vomiting, poor appetite, constipation

  • High blood calcium levels, which can lead to kidney stones, confusion, or heart issues


References


1. Demay MB et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024 Jul 12;109(8):1907-1947.

https://pubmed.ncbi.nlm.nih.gov/38828931/


2. Whiting, S. et al. Dietary Recommendations for Vitamin D: a Critical Need for Functional End Points to Establish an Estimated Average Requirement. J Nutrition. 2005. Vol 135: 304-309.

https://www.sciencedirect.com/science/article/pii/S0022316622100520


3. Zhang, Yu et al. Association Between Vitamin D Supplementation and Mortality: Systematic Review and Meta-analysis. BMJ 2019;366:l4673. 

https://www.bmj.com/content/366/bmj.l4673


4. Giustina A, Bilezikian JP, Adler RA, et al. Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows. Endocr Rev. 2024;45(5):625-654. 

https://pmc.ncbi.nlm.nih.gov/articles/PMC11405507/#bnae009-s0


5. Bolland, Mark J et al. Calcium and vitamin D Supplements and Health Outcomes: A Reanalysis of the Women’s Health Initiative (WHI) Limited-access Data Set. Am J Clin Nutrition. Volume 94, Issue 4, 1144-1149.

https://ajcn.nutrition.org/article/S0002-9165(23)02474-7/fulltext

6. National Institutes of Health. Vitamin D Fact Sheet for Health Professionals. Accessed 9.9.25. 

https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/


Courtney Schmidt
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