Vitamin D Warning Issued as Pharmacist Explains the Common Supplement Mistake to Avoid

Millions of people may turn to vitamin D supplements as the darker autumn and winter months arrive, but taking too much or using supplements incorrectly could cause problems.

The NHS advises people in the UK to consider taking 10 micrograms, equivalent to 400 IU, of vitamin D every day during autumn and winter. This is because there is generally not enough sunlight at this time of year for the body to make all the vitamin D it needs.

While supplements can be a convenient way to maintain vitamin D intake, pharmacists have highlighted two important considerations: how you take the supplement and how much you take.

Vitamin D is a fat-soluble vitamin, so taking it alongside a meal containing some fat may help the body absorb it more effectively. At the same time, taking excessively high doses for long periods can cause vitamin D to build up in the body and potentially lead to serious health problems.

Why vitamin D becomes important in autumn and winter

The body creates vitamin D when skin is exposed to sunlight. During spring and summer, many people can produce much of the vitamin D they need through ordinary exposure to sunlight.

That changes during the colder months.

According to NHS guidance, from October until around the beginning of March, people in the UK do not make enough vitamin D from sunlight.

Vitamin D helps regulate calcium and phosphate in the body. These nutrients are needed to maintain healthy bones, teeth and muscles.

Some people may also need to consider taking a vitamin D supplement throughout the entire year. This includes people who spend very little time outdoors, those who regularly cover most of their skin while outside and people living in settings where they receive limited sunlight.

People with darker skin, including those with African, African-Caribbean or South Asian backgrounds, may also not make enough vitamin D from sunlight and are advised by the NHS to consider taking a supplement throughout the year.

The vitamin D mistake people may be making

How you take your vitamin D supplement can matter.

Vitamin D is fat soluble, which means dietary fat can assist its absorption. Research has found that consuming vitamin D with a meal containing fat can increase absorption compared with consuming it with a fat-free meal.

That means taking a vitamin D supplement alongside foods containing some fat, such as yoghurt, eggs, nuts or avocado, may help with absorption.

This does not mean a supplement taken without these foods is useless. However, taking it as part of a meal can be a simple way of supporting absorption.

Vitamin D is available in several forms, including tablets, capsules, gummies and oral sprays. People should check the label carefully to understand exactly how much vitamin D each dose contains.

Warning over taking too much vitamin D

While getting enough vitamin D is important, taking more than you need does not necessarily provide additional benefits.

Vitamin D can accumulate in the body because it is fat soluble. Consuming excessive amounts for an extended period can result in vitamin D toxicity, sometimes called hypervitaminosis D.

The Cleveland Clinic explains that vitamin D toxicity is rare and is most commonly associated with taking excessive amounts of vitamin D supplements.

The main consequence is hypercalcaemia, where too much calcium accumulates in the blood.

Symptoms can include nausea, vomiting, weakness, constipation, increased thirst, frequent urination and confusion.

In serious cases, excessive vitamin D and the resulting high calcium levels can contribute to kidney problems and abnormal heart rhythms.

How much vitamin D should you take?

For most adults, NHS guidance recommends considering 10 micrograms, or 400 IU, of vitamin D each day during autumn and winter.

There is an important difference between a recommended amount and the maximum amount considered safe.

The NHS says adults should not take more than 100 micrograms, equivalent to 4,000 IU, of vitamin D per day because taking excessive amounts over a long period can cause calcium to build up in the body.

That 4,000 IU figure should therefore not be interpreted as a target daily dose.

Some people may be prescribed higher doses temporarily after a blood test confirms a deficiency. In those circumstances, patients should follow the instructions provided by their doctor or another qualified healthcare professional.

People taking several supplements should also check their labels. A multivitamin, vitamin D supplement and another nutritional product could each contain vitamin D, potentially increasing the total amount consumed each day.

Can you get vitamin D from food?

Vitamin D can also be obtained from certain foods.

Dietary sources include oily fish such as salmon, sardines, herring and mackerel. Egg yolks, liver and some fortified foods can also contain vitamin D.

Certain breakfast cereals and fat spreads are fortified with the vitamin, while some plant-based milk alternatives have vitamin D added to them. The amount varies considerably between products, so checking nutritional labels is useful.

However, obtaining enough vitamin D through food alone can be difficult, particularly during winter.

This is one reason the NHS recommends that people consider supplementation during the months when sunlight cannot provide enough vitamin D.

Don't rely on sunbeds for vitamin D

Trying to increase vitamin D by deliberately exposing yourself to large amounts of ultraviolet radiation is not recommended.

Sunbeds can expose skin to harmful ultraviolet radiation and increase the risk of skin cancer.

Sitting next to a sunny window is not an effective alternative either. Glass blocks most of the UVB radiation involved in the skin's production of vitamin D.

People should therefore avoid excessive UV exposure in an attempt to increase their vitamin D levels.

What to remember this winter

Vitamin D supplements can provide a simple way of maintaining intake during the darker months, but the amount matters.

For most adults, the NHS recommendation is to consider 10 micrograms, or 400 IU, daily during autumn and winter. Taking a supplement with a meal containing some fat may also support absorption.

Most importantly, people should not assume that a larger dose automatically means greater health benefits.

Anyone who believes they may have a vitamin D deficiency, is considering taking a high-dose supplement or has symptoms that concern them should speak to a pharmacist, GP or another qualified healthcare professional.

Sources

[1] National Health Service (NHS), “Vitamins and minerals: Vitamin D,” NHS, UK.

[2] Cleveland Clinic, “Vitamin D Toxicity (Hypervitaminosis D),” Cleveland Clinic, Center for Health Education.

[3] National Institutes of Health, Office of Dietary Supplements, “Vitamin D: Fact Sheet for Consumers,” U.S. Department of Health and Human Services.

[4] B. Dawson-Hughes et al., “Dietary fat increases vitamin D-3 absorption,” Journal of the Academy of Nutrition and Dietetics, vol. 115, no. 2, pp. 225–230, 2015.

Disclaimer

This article is for general informational and educational purposes only and does not constitute medical advice, diagnosis or treatment. Vitamin D requirements can vary according to age, health conditions, medications and individual circumstances. Consult a GP, pharmacist or other qualified healthcare professional before taking high-dose vitamin D supplements or changing prescribed treatment.