At-home vitamin D tests returning ‘unreliable’ results

Which? has warned that rapid vitamin D tests sold for home use could be returning unreliable results and may stop consumers from seeking help for a genuine deficiency.

The consumer body compared the outcomes of rapid self-testing kits against a laboratory blood test and found significant variation between them.

Five widely available rapid vitamin D tests, each costing around £8, were bought by the watchdog for its investigation.

Results from the same person were checked against a Care Quality Commission (CQC) registered laboratory test taken on the same day.

The laboratory test showed vitamin D levels within a sufficient range.

A reading above 50 nmol/L is generally considered a sufficient level of vitamin D.

Rapid tests, however, use a higher cut off of 75 nmol/L to define a sufficient level.

This means more people will be flagged as insufficient by a rapid kit than would be by an NHS-ordered blood test.

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

Only two of the test results in the Which? study suggested insufficient levels.

Two others indicated deficient levels, markedly lower than the level indicated by the researcher's lab blood test.

One test indicated a sufficient level of vitamin D.

An insufficient result indicates a user's levels are below the ideal range.

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.

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.

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.”