At-home vitamin D tests found to return ‘unreliable’ results, watchdog warns

At-home vitamin D tests could be giving unreliable results and preventing consumers from seeking help for a genuine deficiency, a watchdog has warned.

Which? said it found significant variation across rapid self-testing kit results compared with a laboratory blood test.

Vitamin D deficiency is common in the UK, partly because of a lack of adequate sunlight during the winter months, although factors such as diet and age can also play a role.

The watchdog bought five widely available rapid vitamin D tests, all costing around £8.

Results from the same person were compared with a Care Quality Commission (CQC) registered laboratory test taken on the same day, which showed vitamin D levels within a sufficient range.

Anything higher than a reading of 50 nmol/L is generally considered a sufficient level of vitamin D.

Rapid tests use a higher cut off of 75 nmol/L as a sufficient level, meaning more people will be flagged as insufficient compared with an NHS-ordered blood test.

By this measure, the Which? researcher would have been expected to fall within the insufficient range.

However, only two test results in the Which? study suggested insufficient levels, while two others indicated deficient levels – markedly lower than the level indicated by the researcher’s lab blood test.

One indicated a sufficient level of vitamin D.

An insufficient result indicates a user’s levels are below the ideal range while a deficient result suggests levels are significantly lower and could pose a risk to health.

Which? warned that inaccurate results could leave consumers unnecessarily worried about their health, falsely reassured or spending money on high-dose supplements they did not need, potentially putting their health at risk.

The Royal College of Pathologists advises that taking too much vitamin D over time can cause high levels of calcium in the blood with potential complications including kidney stones.

There are also risks to not treating a vitamin D deficiency, as low levels can affect calcium absorption and increase the risk of osteoporosis over time.

When asked, none of the companies provided Which? with specific information about the evidence supporting the test accuracy claims made on their packaging.

Customer reviews also raised concerns about the tests’ usability and difficulty interpreting their results.

Which? shared the findings from its investigation with the Medicines and Healthcare products Regulatory Agency (MHRA).

The regulator confirmed it was reviewing existing regulations, with proposed changes intended to raise standards for self-tests.

Which? said anyone concerned about their vitamin D levels should seek advice from a qualified healthcare professional rather than relying on a rapid home test alone, particularly before making decisions about taking supplements.

Which? head of consumer rights and food policy Sue Davies said: “People turn to at-home health checks for peace of mind and as a way of managing their own health so it is deeply concerning that tests sold by major high street brands and online gave completely contradictory results.

“An inaccurate result risks driving people to spend money on potentially harmful high-dose supplements, or leaving a genuine deficiency untreated.”