Skip to content

Is Vitamin D Over RDA Too Much?

Vitamin D works well beyond just supporting healthy bones and calcium metabolism. Its crucial function extends to your: Hormone balance Metabolism Immune functions Our in-house research and development team identified an important synergy: vitamin D boosts probiotic growth and enhances digestive enzymes’ effectiveness. This discovery is why we incorporate a modest dose of vitamin D…


Vitamin D works well beyond just supporting healthy bones and calcium metabolism. Its crucial function extends to your:

  • Hormone balance
  • Metabolism
  • Immune functions

Our in-house research and development team identified an important synergy: vitamin D boosts probiotic growth and enhances digestive enzymes’ effectiveness. This discovery is why we incorporate a modest dose of vitamin D in the latest version of MassZymes.

We’ve been fielding numerous customer queries regarding the vitamin D3 dosage in MassZymes 4.0—specifically, at 20 mcg or 800 IU per capsule. In this article, we delve into the evidence supporting our choice of vitamin D dosage to address these inquiries. 

Please note that this discussion is informative and not intended as a prescription or a specific dose recommendation.

How Much Vitamin D Should I Take a Day?

The Recommended Daily Allowance (RDA) is a trusted guideline for nutrient intake, but it only gives us the bare minimum of nutrients most healthy people need. The RDA for vitamin D is 600-800 IU . It’s enough to prevent rickets and the deadly levels of deficiency but not enough for optimal health and well-being.

In Personalized Wellness, the best dose of any micronutrient you should take is the dose that gets you in the optimal range. This is also the place where you feel your best, both physically and mentally.

Despite RDA, most of our clients require higher doses to achieve optimal vitamin D blood levels. Instead of guessing your best vitamin D dose, opt for testing. We recommend conducting an initial test and follow-up every 2-4 months to avoid excess vitamin D and to ensure a balanced approach.

While your vitamin D status varies based on numerous factors, deficiency is very common worldwide, especially in temperate climates. Even in tropical regions, people tend to avoid the sun

Learn more about testing your vitamin D levels and factors that can increase your vitamin D deficiency risk in our article: Low Vitamin D: Causes, Prevalence, Nutrigenetics, Supplementation, & More

What Are Optimal Vitamin D Levels?

The truth is that not only can your vitamin D levels be too low, they can also be too high. If it is too low, you risk many concerns, from weak bones and muscles to poor immune function. Too high, you risk above-normal calcium levels, leading to bone pain and kidney issues. Let’s take a look at what a healthy range looks like. 

In a 15-year study involving 15,099 participants, researchers explored the link between vitamin D levels and the risk of death. After accounting for factors like age, gender, and race/ethnicity, researchers determined the lowest risk of death was with vitamin D levels ranging between 73–90 nmol/L (29.9-36 ng/mL).

Researchers also determined that the risk of death significantly rose when vitamin D levels were below 40 nmol/L (16 ng/mL) and, to a lesser extent, above 119 nmol/L (47.6 ng/mL).

It’s important to note that the National Institutes of Health recommends a normal range of 50 nmol/L to 125 nmol/L (20 ng/mL – 50 ng/mL)

. Following this guideline might position you outside the range identified as optimal in the study. Many functional medicine doctors find that patients have better outcomes at a higher range.

How Safe Are Vitamin D3 Doses Over the RDA Levels?

If your vitamin D levels aren’t within the optimal range, you’ll need to take a vitamin D supplement, but how much is too much? Most people don’t have optimal vitamin D blood levels or don’t even know it. Let’s explore the safety of each dose. 

4,000 IU/day

Taking 4000 IU/day of vitamin D is widely accepted as safe and effective as the tolerable upper intake dosage.

A 2023 meta-analysis of 22 studies, including 12,952 participants, examined the long-term safety of taking 4,000 IU/day. Researchers determined that, while largely safe, 4000 IU may


  • Increase the risk of hypercalcemia at a frequency of 4 cases per 1,000 individuals. Hypercalcemia occurs with high calcium levels in your blood, causing symptoms such as nausea, vomiting, weakness, and confusion. 
  • Slightly increase (about 1%) the risk of falls and hospitalization.

Researchers highlighted that most studies of 4,000 IU vitamin D have few participants. They expressed a need for large-scale studies to pinpoint occasional or rare adverse events linked to high doses of vitamin D.

5,000 IU/day

A 5,000 IU/day dose could help prevent or reduce flu-like symptoms while producing minimal adverse events. 

Researchers conducted a 9-month study on 255 healthcare workers to examine whether taking 5,000 IU of vitamin D daily could help prevent flu-like illnesses. Participants who took 5,000 IU of vitamin D daily for at least two months had fewer flu-like illnesses than the control group.


Of the 299 original study participants, five experienced adverse events, including:

  • Burning sensation, oral tenderness, and sun hypersensitivity
  • Intense thirst and frequent urination 
  • Back and leg pain
  • Mouth lesions

Stopping vitamin D supplementation resolved all issues. 

Although the study didn’t measure vitamin D blood levels, knowing the levels would be useful. This would help determine if they were outside optimal levels when experiencing adverse events.

10,000 IU/day

As Vitamin D dosage increases, so do the adverse events. 

A three-year study of 373 healthy adults with vitamin D blood levels close to optimal range aimed to establish whether vitamin D doses up to 10,000 IU/day were safe and well tolerated. Participants took either 400, 4000, or 10,000 IU/day and additional calcium if dietary calcium intake was less than 1200 mg/day. 

Average vitamin D blood levels at three months were as follows:

  • 400 IU daily: 76 nmol/L
  • 4,000 IU daily: 114 nmol/L
  • 10,000 IU daily: 187 nmol/L

The highest vitamin D levels occurred in the 10,000 IU dosage group at 18 months at 343 nmol/L and a peak mean of 198 nmol/L.

Overall, researchers determined that the safety of the dosages was comparable. The study reported mild cases of elevated calcium levels in blood and urine at all dosages but most frequently at the 10,000 IU dosage.

The three dosages didn’t show any significant differences in adverse events. However, it’s important to focus on vitamin D blood levels. Participants taking 10,000 IU daily had levels consistently higher than the optimal range, which could affect their health risks.  

20,000 IU/day or More

20,000 IU daily doses and above are generally reserved for those with additional health issues or severe deficiencies. 

A seven-year hospital study included three patients who took 20,000 to 50,000 IU daily. They all experienced marked improvement in their psoriasis. None of the patients experienced hypercalcemia or any other adverse events.

An additional study of 205 patients at high risk of vitamin D deficiency took 50,000 IU daily for 12 months. After 12 months, the patients experienced an average increase of 52.8 nmol/L in their vitamin D blood levels. They ended up in the optimal vitamin D level range with an average of 82.7 nmol/L (33 ng/mL). The study did not report any adverse effects. 

These studies show that although some people may have negative reactions, vitamin D toxicity is rare. This usually happens when taking extremely high doses, more than 20,000 IU daily.   

Some factors can influence your daily dose of vitamin D. People more likely to require a higher dose include :

  • Older adults
  • Those with limited sun exposure
  • Those with darker skin
  • Health conditions that limit your fat absorption
  • Obesity or undergoing gastric bypass surgery
  • Those with inflammatory health conditions

You can learn more about what factors may require a higher dose to reach optimal levels in this article

Who Needs to Avoid High Doses of Vitamin D?

High doses (>4000 IU) of vitamin D may not be suitable for everyone. It’s crucial to consult with your doctor, especially if you have kidney issues or are taking medications like:

  • Cholesterol-lowering drugs
  • Steroids
  • Medications for blood pressure control
  • Certain heart medications


Taking 4,000 IU is generally considered safe. When taking vitamin D supplements, some important things to keep in mind include:

  • Higher doses may be necessary for optimal vitamin D levels.
  • Consult a medical professional and undergo seasonal blood vitamin D testing.
  • Ensure balance by incorporating complementary nutrients like magnesium, calcium, and vitamin K2.

Share this article using the buttons below
  1. Vitamin D. (n.d.). Retrieved January 5, 2024, from
  2. Dominguez, L. J., Farruggia, M., Veronese, N., & Barbagallo, M. (2021). Vitamin D Sources, Metabolism, and Deficiency: Available Compounds and Guidelines for Its Treatment. Metabolites, 11(4).
  3. Sempos, C. T., Durazo-Arvizu, R. A., Dawson-Hughes, B., Yetley, E. A., Looker, A. C., Schleicher, R. L., … Picciano, M. F. (2013). Is there a reverse J-shaped association between 25-hydroxyvitamin D and all-cause mortality? Results from the U.S. nationally representative NHANES. The Journal of Clinical Endocrinology and Metabolism, 98(7), 3001–3009.
  4. Zittermann, A., Trummer, C., Theiler-Schwetz, V., & Pilz, S. (2023). Long-term supplementation with 3200 to 4000 IU of vitamin D daily and adverse events: a systematic review and meta-analysis of randomized controlled trials. European Journal of Nutrition, 62(4), 1833–1844.
  5. van Helmond, N., Brobyn, T. L., LaRiccia, P. J., Cafaro, T., Hunter, K., Roy, S., … Chung, M. K. (2022). Vitamin D3 Supplementation at 5000 IU Daily for the Prevention of Influenza-like Illness in Healthcare Workers: A Pragmatic Randomized Clinical Trial. Nutrients, 15(1).
  6. Billington, E. O., Burt, L. A., Rose, M. S., Davison, E. M., Gaudet, S., Kan, M., … Hanley, D. A. (2020). Safety of High-Dose Vitamin D Supplementation: Secondary Analysis of a Randomized Controlled Trial. The Journal of Clinical Endocrinology and Metabolism, 105(4).
  7. McCullough, P. J., Lehrer, D. S., & Amend, J. (2019). Daily oral dosing of vitamin D3 using 5000 TO 50,000 international units a day in long-term hospitalized patients: Insights from a seven year experience. The Journal of Steroid Biochemistry and Molecular Biology, 189, 228–239.
Posted in
You'll enjoy these posts


  1. Maria on January 7, 2024 at 10:37 pm

    It is my understanding that Vitamin D must be taken with K2 in order to keep the calcium in the bone tissue, thus strengthening your bones and not causing hypercalcemia. That wasn’t mentioned in any of the studies above. Others still promote the use of all of the fat soluble vitamins (D, A, K1 K2, E) be taken together rather than only one or two as they each work in tandem with the others. Any thoughts on this?

Leave a Comment