What Drugs Should Not Be Taken With Vitamin D?

Vitamin D is an essential part of maintaining a healthy diet. It is particularly important for building bones and keeping them strong. This is because it helps to absorb calcium and phosphorus,¹ which are some of the key components of healthy bones. However, there are a number of medications that interact with vitamin D – this usually results in excess absorption of these medications, which can have harmful effects on the body, such as oestrogen and thiazides.²

There are some drugs that can also lower vitamin D absorption: 2

• antacids
• calcium channel blockers
• cholestyramine
• some anticonvulsant medications
• mineral oils

Excess vitamin D in the blood can be harmful as this can cause a harmful build-up of calcium in the body. This can cause weakening of the bones and damage to organs like the heart and kidneys.³

There are many benefits to taking vitamin D in moderation, which will be discussed further. However, there are also interactions of these drugs that can result in vitamin D increasing to toxic levels in the body and can have harmful consequences. 

The importance of vitamin d in our health

Vitamin D is important in the building and maintenance of healthy bones. The bones support the entire body and allow us to stand upright; therefore, they need to be able to withstand a lot of force to ensure that they are able to carry out this function.³

The teeth are also part of the skeleton and are, therefore, bone. Vitamin D ensures that the teeth are strong and healthy so that they are able to break down food.³

Vitamin D also ensures that the muscles remain healthy. When a person uses their muscles intensely, for example, when lifting something heavy, the muscles can sustain damage. Vitamin D can aid in many processes to ensure that the muscles regenerate properly so that their structure is maintained. ⁴ One of the ways it does this is by allowing the mitochondria (which are structures that make energy in cells) to work properly.

If a person has low vitamin D levels, it can lead to osteomalacia, which is a condition in which the bones become soft due to low vitamin D (and, as a result, calcium) levels. In children, this may manifest as rickets. This also causes softness of bones but may cause deformities as children’s bones are still developing.

Where can we get vitamin d?

Vitamin D can come from a variety of sources, whether that be through diet, sunlight or supplements. It is typically better to aim to get the daily intake of food as part of a healthy diet or from the sun.

Some food that contains vitamin D include:³

• oily fish
• egg yolks
• some cereals which have been fortified – this means that there is added vitamin D

The sun is another important source of vitamin D. Our skin absorbs the UV rays from the sun. This then goes through a multi-step process which results in it being converted to vitamin D. In the summer months, humans can usually get enough vitamin D from the sun and their diets to provide sufficient amounts for the body.

However, when the winter months roll around, especially if a person lives in a country where there is little sunshine, like the United Kingdom, the general advice is to take supplements to ensure that the body is adequately supplied with vitamin D.  

When to take vitamin d

The sun and diet are usually enough to ensure there is enough vitamin D. However, in the winter months, when there is less sunshine, taking vitamin D supplements is generally advised. This is especially true for people who are more likely to develop a vitamin D deficiency, for example, newborn babies and pregnant women.

Some people may experience difficulty absorbing vitamin D for various reasons and thus may be at high risk of developing a deficiency. For these people, vitamin D supplements may be prescribed year-round to ensure that they do not develop any illnesses associated with vitamin D deficiency.

What medications should not be taken with vitamin d?

In the body, drugs are able to interact with each other. This may result in one drug being absorbed at a different rate than it usually would. For this reason, it is advised to check with a doctor before taking any new supplements, just in case there are some interactions.

There are some drugs that will increase vitamin D absorption, which is problematic as this can lead to harmful levels of calcium in the blood (hypercalcaemia), which can eventually lead to damage to the bones, heart and kidneys.

Some drugs can lower the rate of vitamin D absorption, which is an issue as this means that, even with supplementation, there is not enough vitamin D in the body. This can cause vitamin D levels to drop further, putting people at risk of osteomalacia.

The drugs that cause an increase of vitamin D in the blood are:

• oestrogen – this is a hormone which is used in a variety of therapies such as hormone replacement therapy and birth control
• thiazides – this a class of diuretic drugs (meaning they make a person need to urinate more)

The most important of these is the thiazides. Thiazides will concentrate more sodium (a salt that makes up half of the salt that people like to put on chips) into the urine, allowing more water to flow into the urine. However, the thiazides act on a specific pathway that makes the kidneys hold onto calcium rather than expelling it through the urine.⁵

As mentioned above, vitamin D also works to increase the absorption of calcium, creating higher levels of it in the blood. As a result of both of these factors, calcium can quickly rise to dangerous levels in the blood, giving rise to the consequences associated with hypercalcaemia. 

Oestrogen has been shown to have a positive correlation with vitamin D – this means that as vitamin D increases, so does oestrogen, and they also decrease together.⁶ This is interesting as it means that the two may be linked and that the absorption of one may also affect the other. The combination of the two is thought to have favourable effects on blood pressure, blood sugar and fat levels.

There are also some drugs that can affect blood levels of vitamin D:

• antacids – these are used for common issues such as heartburn
• calcium channel blockers – these may be used to lower blood pressure
• cholestyramine – this can lower cholesterol in the blood
• some anticonvulsant medications – these may be used to treat seizures
• mineral oils – these may be applied topically as a moisturiser, or may be used as a laxative

The specific class of antacids that prevent vitamin D absorption are H2 blockers, which affect the ability of the stomach cells to produce acid.⁷ Furthermore, aluminium-based antacids can be absorbed too strongly as a result of vitamin D and so may result in aluminium poisoning.⁸

Calcium channel blockers slow the rate at which calcium is used, specifically in the heart.⁹ This may be problematic if a person takes vitamin D at the same time as the calcium in the blood is being used slower, and vitamin D will increase this, potentially causing dangerous side effects.

Cholestyramine is a cholesterol-lowering drug that works by lowering the amount of bile in the body. Bile helps to absorb fats. However, as vitamin D is a fat-soluble vitamin, it is not absorbed well when taken with cholestyramine.⁸

Anticonvulsants may cause vitamin D to be used quicker in the body.²

Mineral oil, when used to aid with constipation, may slow the absorption of vitamin D. This is because vitamin D is a fat-soluble compound and dissolves in mineral oil. This means vitamin D spends longer in the stomach and intestines rather than being absorbed into the blood.⁸

Summary

Vitamin D is vital for the correct functioning of the body as it plays a role in many processes. Most notably, these processes involve the growth, maintenance and repair of bones and muscles. As a result, ensuring that people get enough of it is important. The main sources of vitamin D are the sun, diet and supplements. Supplements are usually taken around the autumn and winter seasons when there is less sunshine. This, for most people, can help maintain healthy levels of vitamin D throughout the year.

 However, for some people on specific medications, there may be interactions that can prevent vitamin D from being absorbed or may result in too much vitamin D or calcium being absorbed into the blood. This can quickly become dangerous as such people may suffer from hypercalcaemia, which can cause damage to the bones, heart and kidneys.

 It is important to seek advice from a doctor before starting any new medication, including ones that are generally perceived as ‘harmless’, such as vitamin supplements. This is because of the interactions between different drugs.