Vitamin D Side Effects

The U.S. Food and Drug Administration (FDA) does not have any strict guidelines on supplements and herbs. This means that it is impossible to guarantee the safety, purity or strength of products and it also means that effects can vary a lot. This is why it is so important to always read the label and to never take any products without consulting with a healthcare provider first, particularly if you have a medical condition. If you do take something and experience side effects, you must also seek medical advice straight away. This is also true for vitamin D, known as the ‘sunshine vitamin’.

What Is Vitamin D?

This vitamin can be found in a number of foods naturally, particularly in oily fish. Many dairy products and juices are also fortified with it. However, between 80% and 90% of all vitamin D that humans get comes from the sun.

When vitamin D was first research, scientists found that it was hugely important in the prevention of rickets, an illness that causes soft and weak bones. Later on, it was quickly found to be responsible for the protection of many other things as well, not all relating to bones and teeth. Today, we know that it is vital to protect the heart and blood, prevent high cholesterol and blood pressure, treat obesity, diabetes, multiple sclerosis, muscle weakness, COPD, rheumatoid arthritis, bronchitis, asthma, PMS and gum and tooth disease. Additionally, it has benefits for the skin, helping reduce the symptoms of lupus vulgaris, actinic keratosis, psoriasis, scleroderma and vitiligo to name but a few. Finally, it boosts the immune system, helping people with various autoimmune disorders and even helps to prevent certain types of cancer.

How Does Vitamin D Work?

Vitamin D gets to work in our body by regulating levels of phosphorus and calcium. The best way to assist it in doing this is by getting regular sun exposure. Spending just 15 minutes a day, four times a week, with direct sunlight exposure is generally enough, although this does depend on geographical location.

Unfortunately, at least 60% of our population has a vitamin D deficiency. This is due to a number of reasons, but mainly the fact that people simply do not get out in the sun enough anymore. And when they do, they often put on sunscreen lotion. Various population groups are at particular risk, including those of a darker ethnicity, the elderly and the obese. Interestingly, in South Florida, the Sunshine State where so many elderly people retire, deficiency rates among people are still as high as 40%.

As a result, it is now recommended that all people, regardless of age, gender, ethnicity or geographical location, take vitamin D supplements. The supplements are available without prescription and are very affordable. However, this brings us back to the lack of regulation, which is leading to people not truly knowing how much they are taking. Furthermore, most people – including scientists – don’t truly know how much should be taken.

Vitamin D Side Effects

According to scientists, vitamin D is “likely safe” if it is taken orally or if it is injected by a medical professional. It is very rare for people to experience side effects, but it isn’t unheard of. This is particularly true in those who take too much. Some of the possible side effects include:

• Fatigue
• Weakness
• Headaches
• Sleepiness
• Dry mouth
• Loss of appetite
• Nausea
• Metallic taste
• Vomiting

Some research now suggest people should take as much as 4,000 IU daily. However, this is highly controversial research and many scientists do not subscribe to this. In fact, they suggest that taking as much as this is “possibly unsafe”, because the levels of calcium in the blood can reach very high levels. On the other hand, if done under medical supervision in order to treat a severe deficiency, it is classed as safe.

Special Precautions and Warnings for Vitamin D

A number of warnings do exist for taking vitamin D, as described in the table below.

Condition Precautions and Warnings
Pregnant or nursing mothers So long as the UI stays below 4,000, vitamin D is “likely safe”. If higher dosages are taken, however, it is “possibly unsafe”. Worryingly, one school of thought says that taking higher amounts can increase the risk of birth defects. The other school of thought says the opposite, mainly that it reduces the risk of complications.
Kidney disease Because vitamin D increases levels of calcium, it can lead to ‘hardening of the arteries’. At the same time, without sufficient vitamin D, renal osteodystrophy can occur. Hence, people with kidney disease must speak to medical professionals.
High calcium levels Taking any dosage of vitamin D can make this worse.
Atherosclerosis This is a condition whereby the arteries harden. It is common in those with kidney disease. Vitamin D could worsen this condition.
Sarcoidosis Calcium levels can increase by taking vitamin D, leading to kidney stones. It is important to use the vitamin with caution.
Histoplasmosis Vitamin D can raise levels of calcium, possible leading to kidney stones. Must be used with caution, therefore.
Hperparathyroidism Vitamin D must be used with caution due to a possible increase in calcium levels
Lymphoma Vitamin D can raise levels of calcium, possible leading to kidney stones. Must be used with caution, therefore.
Tuberculosis Vitamin D can raise levels of calcium, possible leading to kidney stones. Must be used with caution, therefore.

Vitamin D Drug Interactions

It is equally important to be aware of the fact that vitamin D, particularly supplements, can interact with other drugs. The table below explains the potential risks.

It is equally important to be aware of the fact that vitamin D, particularly supplements, can interact with other drugs. The table below explains the potential risks.

Interaction Drug Effects
Moderate Aluminum This is found in the majority of antacids and can increase body absorption. This can be dangerous for people who have kidney disease. If vitamin D is necessary, it should be taken four hours after antacids, or two hours before.
Moderate Calcipotriene/Dovonex Calciportiene is actually very similar to vitamin D. This means that the effect is increased, as is the chance of side effects, by taking them both.
Moderate Digoxin/Lanoxin Vitamin D ensures your body can properly absorb calcium. The heart can be affected by calcium. Digoxin makes the heartbeat stronger, which means effects may be stronger if vitamin D is taken alongside it. This could lead to an irregular heartbeat. Only take vitamin D if recommended by your physician.
Moderate Diltiazem/Cardizem/Dilacor/Tiazac These drugs and vitamin D can affect the heartbeat. Vitamin D often lowers the effectiveness of the drugs.
Moderate Verapamil/Calan/Covera/Isoptin/Verelan Again, these drugs affect the heart, as can calcium. Hence, vitamin D should only be taken in very low quantities.
Moderate Water pills/thiazide diuretics Water pills often raise levels of calcium. This means that, if taken with vitamin D, there may be too much calcium in the body, leading to very serious side effects including kidney issues.
Minor Cimetidine/Tagamet Cimetidine can lower the body’s ability to convert vitamin D. Hence, the supplement will be less effective.
Minor Heparin Heparin can increase the chance of breaking bones. This is why people should certainly take even more vitamin D (as described by physicians, however).
Minor LMWHS These drugs can increase the chance of breaking bones. As with Heparin, therefore, it is generally recommended to supplement with vitamin D.

Vitamin D – Pregnancy and Breastfeeding

It is very important that women who are pregnant or breastfeeding receive adequate levels of vitamin D. However, the jury is still out on just how much is an ‘adequate’ amount. Most agree that it is between 2,000 and 4,000 IU, but the question is where on that scale the right level is, particularly since most supplements and natural sources are much lower than those recommended UIs. Additionally, levels should drop significantly if women are breastfeeding, and levels also depend on whether someone takes a vitamin D combination, D2 or D3.

Resource and References:

Vitamin D – How to take vitamin D and possible interactions. (University of Maryland Medical Center)
Vitamin D – General information on vitamin D. (Everyday Health)
Am I Getting Too Much Vitamin D? – Possibility of vitamin D overdose. (Vitamin D Council)
Vitamin D – Vitamin D supplements. (Medicine Net)
Vitamin D Side Effects – Possible side effects of vitamin D supplementation. (
Vitamin D Supplementation for Women During Pregnancy – Vitamin D supplements for pregnant women. (WHO)