What Are The Side Effects of Vitamin D Supplements?

When we hear the phrase side effects, we straight away think of pharmaceutical treatments, our thoughts rarely go to dietary aids like vitamin D supplements. Most of you might be ruling out the possibility of side effects with vitamins such as this due to their beneficial composition, but it can, in fact, happen. 

According to Pieter Cohen, M.D., a professor at Harvard Medical School specializing in supplement safety,  the reason for the ignorance of side effects lies in the fact that they are sold— "as openly and as freely as food." And just like other industry experts, he agrees they should be more recognized for better and safer supplementation journeys. 

So let's get into them below:

Key Findings

  • Common side effects linked to vitamin D supplementation are mild and manageable.
  • Excessive vitamin D supplementation can trigger serious side effects like excessive calcium absorption, calcium deposition, and impaired kidney function.
  • Vitamin D supplements can have a diuretic effect—increases urine production, which leads to other more intense side effects.

Why Do Vitamin D Supplements Trigger Side Effects

I'm sure you're wondering how a vitamin D supplement meant to fill or bridge a nutritional gap can trigger side effects. According to experts, the issue lies in the active ingredients ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3), which are present in vitamin D supplements. 

Here are some reasons why these active components can cause side effects:

Supplementation familiarity

The active components of vitamin D supplementation are quite potent, so the body can be a bit overwhelmed by its effects. The most common side effects of vitamin D supplements happen because the body is trying to keep up with the change the supplement provides. Once caught up and familiar with the effects, the body settles down, and the side effects disappear.

Excessive calcium absorption

Vitamin D plays a crucial role in calcium absorption from the intestines. When taken in excess, it can increase calcium absorption beyond what is needed, leading to elevated calcium levels in the blood leading to side effects. However, Vitamin K can help regulate calcium and direct it to the right places, preventing side effects associated with excessive calcium.

Calcium deposition

High vitamin D levels can cause excess calcium to be deposited in various tissues, such as blood vessels, kidneys, and soft tissues. This can contribute to developing conditions like kidney stones and calcification (a process where calcium builds up, causing the tissue to harden blood vessels), a more serious set of side effects. Again, adequate vitamin K may help regulate calcium and prevent these side effects.

Kidney function

Like other supplements, Vitamin D is processed (metabolized and activated)  through our kidneys. If we inappropriately supplement vitamin D, it can strain our kidneys, which leads to side effects.

Interaction with medications and contraindications with other conditions

Vitamin D can interact with certain medications and conditions, leading to an increased risk of side effects.

While rapidly increasing vitamin D intake for the benefits seems like a great idea, it shouldn't be done as it can support the processes mentioned above and trigger side effects that can cause you more harm than good. Following RDAs (recommended dietary allowance) or advised doses that factor in your age, lifestyle, health conditions, and more is important. Regular monitoring of vitamin D levels through blood tests is also recommended to ensure optimal supplementation without exceeding safe limits.

Side Effects Linked to Vitamin D Supplement Use

Now that you know how vitamin D supplements can trigger side effects, let us look at the culprits themselves—the different side effects that may occur when you use vitamin D supplements. Side effects include:

Digestive issues

Some individuals may experience gastrointestinal disturbances such as nausea, vomiting, constipation, or diarrhea when taking high doses of vitamin D.


Vitamin D can have a diuretic effect which means it increases urine production. This may lead to increased water loss, resulting in dehydration, dry mouth, headaches, and weakness if adequate fluid intake is not maintained.

This condition develops when too much calcium is in the blood (vitamin D enhances calcium absorption). It usually occurs when excessive doses of vitamin D are taken for a prolonged period. The symptoms of this condition can trigger abdominal pain, muscle weakness, confusion, nausea, vomiting, excessive thirst, and frequent urination.

Besides hypercalcemia, the other side effects are considered mild and common as they are experienced often. However, if their intensity increases and other adverse effects join in, more serious issues might be behind them, and professional help must be sought out.

How to Lower the Possibility or Intensity of Side Effects When Taking Vitamin D Supplements

A study in the New England Journal of Medicine showed that a whopping  23,000 people wind up in the emergency room each year due to adverse effects caused by supplements. While the type and intensity of side effects differed from user to user, most of them could be avoided or alleviated before they grew in intensity if users were more aware of what to do to alleviate them.

If you experience side effects from vitamin D supplements, there are several steps you can take to alleviate them. Let's look at some of the steps below:

Try symptomatic relief

For mild symptoms like nausea, vomiting, diarrhea, headaches, dry mouth, and other digestive issues, try using natural DIY solutions. For example, nausea can be combated by eating dry crackers, hydrating regularly can help with headaches and dehydration, and digestive discomfort can be eased by taking the supplement with food. Food can also aid in absorbing fat-soluble vitamins like vitamin D. So, look at the symptom and find individual solutions.

Adjust the dosage

 If you're experiencing moderate side effects, adjusting the dosage of your vitamin D supplement may be necessary. Read up on recommended doses and successfully alter them. Do a bit of trial and error and see which dose doesn't trigger side effects.

Split the dosage

 If you're taking a high-dose vitamin D supplement, splitting the dosage into two smaller doses throughout the day may help minimize side effects. This can potentially reduce the peak levels of vitamin D in the blood, which may contribute to the side effects.

Consider different formulations

Vitamin D supplements are available in different forms—capsules, tablets, liquids, or chewable tablets. If you're experiencing difficulty swallowing or have gastrointestinal issues with a particular form, you could try a different formulation that may be more suitable for you and eliminate the side effects being experienced.

Review other medications and conditions

If you're taking other medications alongside vitamin D supplements or you have underlying medical conditions, check if they aren't ticking off the interaction or contraindication boxes of vitamin D supplements. If they are, you need to look for appropriate alternatives to stop side effects from occurring.

If you continue to experience persistent or severe side effects despite these measures, then professional evaluation is needed, and a more tailored solution to alleviating side effects or discontinuing vitamin D supplementation is required.

Final Word  

After doing intensive research and breaking down the facts, I conclude that the presence of side effects doesn't necessarily mean you need to stop taking your vitamin D supplement. Their presence and specific details about them can tell us why they occur and how to solve them. Depending on these factors, we can opt for DIY solutions, dose adjustments, medication alternatives, or discontinue use if severe side effects point in that direction (and look for other sources). By paying close attention to side effects, we don't have to unnecessarily miss out on the supplement's benefits.

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About the Author

Sam is a passionate health and fitness enthusiast who has been interested in supplements, fitness, and wellness for over 10 years. He is the founder of Great Green Wall - the health and wellness brand and has completed multiple fitness certificates, including personal training and nutrition certifications. Sam has been working as a personal trainer for the past three years and is dedicated to helping his clients achieve their fitness goals and lead healthier lifestyles. He believes that a healthy lifestyle is crucial to a happy and fulfilling life and is committed to sharing his knowledge and passion with others.

    • Hi Kenn,

      Thank you for your interest in the sources of information!

      All the references and sources used for the information in this article are hyperlinked directly in the text. If you see any underlined text, that’s a hyperlink which will take you directly to the original source of the information. This way, you can delve deeper into the research and data at your own convenience.

      I hope this clarifies your query.

      Kind regards,

    • Hi Rosemary,

      In general, it’s safe to take these two supplements. However, everyone is unique and may respond differently to supplements.

      That’s why it’s vital to always get in touch with your healthcare provider before diving into a new supplement routine. Particularly if you’re already on some medications or managing underlying health issues, personalized advice from your healthcare provider becomes critical. It’s important to remember that the dosage and timing of taking these supplements can differ based on individual needs, and no one knows this better than your healthcare provider.

      As always, stay healthy!

    • Hi John,

      Good question! The amount of vitamin D can depend on a lot of variables like your age, your diet, lifestyle and how much sun you get.

      We have a whole article about it which I think can give you some answers. You can read here. I think you’ll find it helpful!

      Kind regards,

  • Seems to me that the side affects far outweigh the benefits, yet you still suggest we keep taking them. This is the perfect example of the pharmaceutical industry’s rationale for us all. Maybe we should just consume foods that are high in vitamin D? Vomiting, diarrhea, stomach pain and headache do not seem like “mild side affects.” Just saying.

    • Hi Red,

      You’ve raised a really good point! Vitamin D supplements, just like any supplement, can have side effects, especially if taken in large doses. However, it’s important to remember that many people take vitamin D supplements without experiencing any negative effects, and for many, the benefits in terms of bone health, immune function, and other aspects of wellness can be significant.

      That said, you’re absolutely correct that getting nutrients from food is usually the best approach when it’s feasible. Foods like fatty fish, cheese, egg yolks, and foods fortified with vitamin D are all great options.

      The key is to balance your nutrient intake based on your specific needs, and to always consult a healthcare professional for guidance. It’s also worth noting that the side effects you mentioned typically occur when vitamin D is taken in very high doses, well above the recommended levels.

      Remember, this information is general in nature, and individual health needs can vary widely, so it’s always good to speak to your healthcare provider for any specific questions.

      Kind Regards,

    • Hi Fran,

      great question! The ‘right’ amount of vitamin D can depend on a lot of variables like your age, your diet, lifestyle and how much sun you get.

      We have a whole article about it which I think can give you some answers. You can read here. I think you’ll find it helpful!

      Kind regards,

    • Hi Terry,

      Good question! The vitamins you should be taking daily will really depend on your particular needs, lifestyle, diet, overall health, etc. Generally, a balanced diet that contains fruits, vegetables, proteins, and whole grains should provide most of the vitamins your body needs.

      For some people, a multivitamin can be a good way to fill in any nutritional gaps. Specific vitamins or supplements might also be recommended based on individual needs, for example Vitamin D for people that get limited sun exposure or B12 for vegans.

      However, it’s very important to remember that supplements are not a substitute for a healthy diet and lifestyle. It’s always a good idea to consult with a healthcare provider before starting to take any supplement.

      Stay healthy!

  • Finally someone who tells the truth. I took vitamin d for years and had bone LOSS with this supplement. I tried several brands, doses, and even pulsing. My calcium was high, which can mean several things, but mine was from the vitamin d. It’s better now that I’ve quit using it. I had several other problems with vitamin d also, i couldn’t walk well after sitting, it truly caused me to be diagnosed with osteopenia at an early age, and it looked like i was peeing my bones away in my urine. I was so inflamed among other things. I’d like my numbers to be higher, but I have to settle for getting my vitamin d from food and sunshine. It sounds crazy, but I’ve met a nurse administrator and a friend who had the same issues, so that helped me realize I’m not alone. It seems most can tolerate it, I absolutely can not. Thanks for the article.

  • I do have calcium in my blood, I did visit with an endocrinologist and she was the one who recommended taking vita d 3, your thoughts?
    Thank you!!

    • Hi Lynda,

      Thanks for sharing your situation! If your endocrinologist recommended taking Vitamin D3, it’s likely based on a thorough understanding of your specific health needs and conditions. Vitamin D3 plays a significant role in helping the body absorb calcium, which is essential for bone health and other things.

      However, as with any supplement, it’s always important to take it as directed by your healthcare provider and monitor for any unusual symptoms or side effects.

      While I strive to provide useful health information, I always emphasize that your healthcare provider’s advice should be paramount as they understand your individual health situation best.

      Kind regards,

    • Hi Ana,

      It’s important to discuss this matter with your healthcare provider, especially considering your age and specific circumstances. I provide general information, but I can’t provide personal medical advice.

      However, I can tell you that vitamin D plays a critical role in several body functions, including bone health, and it’s often used as a supplement, especially in older adults. The daily dosage varies depending on individual needs and circumstances.

      But remember, any changes in your medication or supplement regimen should always be discussed and supervised by a healthcare professional who knows your medical history. Don’t discontinue any medication or supplement without consulting with them first.

      Stay healthy!

  • Hello Sam my name is Ahesia , I’m 46 year’s old.I live in Fresno CA, and I have a vitamin D deficiency.my Dr prescribe me with some vitamin d supplement that I have to take by mouth one every week and she also advised me to go outside and get some sun but I wanted to know how long do I have to be outside everyday (which I know sun gives us vitamin d as well.

    • Hi Ahesia,

      You’re correct, sunlight does indeed help our bodies produce vitamin D!As for how long you should stay outside for optimal vitamin D production, it can vary based on several factors such as the time of year, time of day, your skin type, and even the amount of skin exposed.

      A general recommendation often cited is about 10 to 30 minutes of sunlight, several times per week. Most people can make enough vitamin D with some parts of their bodies exposed in this time frame.

      Please remember, though, that while sunlight is a good source of vitamin D, it’s also important to be mindful of the risks of excessive sun exposure, such as skin cancer. Always protect your skin if you plan to be outside for prolonged periods. Also, bear in mind that the sun’s rays are strongest between 10 a.m. and 4 p.m.

      Lastly, this information is a general guide, and individual needs can vary. It’s always best to discuss your specific circumstances and concerns with your healthcare provider to get the most accurate advice.

      If you want some more information on Vitamin D dosages, we have a great article about it. You can find it here.

      Stay safe!

  • I am still taking Vitamin D2 (50,000 units) since 2008 because I was diagnosed with a Total Thyroidectomy.
    I am diagnosed with CKD, stage 3b. The question is: should I stop taking this medication?

    • HI Susan,

      Thank you for reaching out and sharing your situation. It’s really important, especially when it comes to medication and health conditions, that you consult with a healthcare professional who is familiar with your specific circumstances. I can provide general information, but I can’t provide medical advice.

      Vitamin D can have different impacts on different people, particularly when conditions like Chronic Kidney Disease (CKD) are involved. Additionally, your thyroidectomy may also impact how your body processes medications and supplements, so it’s crucial that you discuss this with your healthcare provider, preferably one who is familiar with your case.

      Kind Regards,

  • I have been taking Vit D3 25mcg tabs for sometime. Recently I have been getting dizzy spells & headaches. Could this be a side effect.

    • Hi Mrs Patricia,

      Thanks for sharing your experience with us. I’m sorry to hear you’ve been feeling unwell.

      While it’s hard to say for sure if your dizziness and headaches are related to your Vitamin D3 intake, it is certainly a possibility.

      I’d really recommend getting in touch with a healthcare provider who can help figure out what might be going on. They can assess whether these symptoms are related to your Vitamin D supplementation or if there’s another cause that needs to be addressed.

      Remember, we’re here to provide information, but your doctor is the best person to turn to for personal medical advice.

      Take care,

  • Will combining D3 and K2 in one capsule prevent the depositing of Calcium in the bloodstream and walls of the blood vessels, in fact prevent the deposits and instead transport the Calcium to skeletal system?
    If so, is it advisable to take the combined supplement throughout the year, not only during the Winter months?

    • Hi Edward,

      Vitamin D3 and K2 do indeed work together in calcium metabolism. D3 helps absorb calcium, and K2 guides it to the bones, potentially preventing deposits in blood vessels.

      Whether to take a combined supplement year-round will depend on many factors like diet, sun exposure, and individual health, so I suggest you consult with your healthcare provider so they can help you with a tailored answer to your particular needs. This article only provides general information.

      Kind regards,

  • Wow, this is a great read. I’ve been on a 1,000IU for 11 yrs now because of breast cancer & still taking the same amount. I didn’t know you could be tested for vitamin D levels & I’m going to ask my Dr for the blood test.

    • Hi Paul,

      Indeed, taking Vitamins K2 and D together can potentially mitigate certain adverse effects. They often work in concert; Vitamin D enhances calcium absorption, while Vitamin K2 guides this calcium to the bones and helps prevent it from depositing in the arteries.

      However, always keep in mind that each person’s health requirements are unique. Therefore, it’s always wise to consult your healthcare provider before starting any new supplement regimen.

      Stay healthy,

  • State the studies.
    You don’t mention what “excessive “amounts are in numerical values such as IUs.
    Making a statement as ambiguous as :” 23,000 people wind up in the emergency room each year due to adverse effects caused by supplements” does not prove anything,you don’t clarify how many from Vitimin D. It’s as if you are working for big pharma. Pharmaceutical drugs have far worse side effects than any natural supplement.why don’t you mention that as a comparison?
    Thanks but no thanks to your ” extensive” research which you could have easily posted links to!

    • Hi Oliver,

      I apologize if any part of the article was unclear. You’re correct, providing more specific information and referencing the studies directly can offer a more complete picture.

      To clarify, all the studies and research referred to in the article are indeed linked within the article. If you scroll through, you’ll find each study explained backed up by a hyperlink that leads to the source of the information. You can click on these links to see the original studies and research for a more detailed understanding.

      Again, I appreciate your feedback. We strive to offer thorough and reliable information, and the sources are provided for full transparency.

      If there’s anything else you’d like to know, feel free to ask.

      Thank you,

    • Hi Kris,

      Yes, taking vitamin D with vitamin K can aid calcium absorption and utilization. Vitamin D boosts calcium absorption from food, while vitamin K directs the absorbed calcium to the bones and prevents it from depositing in arteries. Together, they promote bone and cardiovascular health.

      Kind Regards,

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