Home vitamin D checks found to produce ‘unreliable’ readings, watchdog warns

Which? said it found major differences between rapid self-test results and a laboratory blood test.

At-home vitamin D tests may be producing unreliable results, potentially stopping people from getting help for a real deficiency, a watchdog has warned.

Which? said it found major variation in the results from rapid self-testing kits when compared with a laboratory blood test.

Vitamin D deficiency is common in the UK, partly because of limited sunlight during the winter months, although diet and age can also be factors.

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

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

In general, a reading above 50 nmol/L is considered sufficient.

Rapid tests use a higher threshold of 75 nmol/L as the cut-off for sufficiency, so more people are likely to be told their levels are low than with an NHS-ordered blood test.

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

But in the Which? study, only two results suggested insufficient levels, while two others indicated deficient levels — far lower than the level shown by the researcher’s laboratory blood test.

One test suggested a sufficient level of vitamin D.

An insufficient result means a user’s levels are below the ideal range, while a deficient result suggests levels are significantly lower and may threaten health.

Which? warned that inaccurate results could leave consumers worried unnecessarily, falsely reassured, or paying for high-dose supplements they do not need, potentially putting their health at risk.

The Royal College of Pathologists says taking too much vitamin D over time can raise calcium levels in the blood, with possible complications including kidney stones.

There are also risks linked to failing to treat a vitamin D deficiency, as low levels can affect calcium absorption and raise the risk of osteoporosis over time.

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

Customer reviews also raised concerns about how easy the tests were to use and how difficult the results were to interpret.

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

The regulator said it was reviewing existing rules, with proposed changes aimed at raising standards for self-tests.

Which? said anyone worried about their vitamin D levels should seek advice from a qualified healthcare professional rather than relying on a rapid home test alone, especially before deciding whether to take 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.”