Researchers in Dublin have become the first in the world to report successfully measuring vitamin D in human hair. This could pave the way for improving the diagnosis of vitamin D deficiency.

Vitamin D deficiency has long been linked with poor bone health, but it may also be a risk factor for a range of other conditions, including depression, diabetes, cardiovascular disease and cancer.

The main source of vitamin D is ultraviolet B (UVB) radiation from the sun, however this can be affected by factors such as sunscreen use, cloud cover and seasons.

The vitamin is also found in certain foods such as oily fish like mackerel and salmon, cheese, egg yolks and foods fortified with vitamin D, such as milk and cereals.

According to the researchers from Trinity College Dublin (TCD) and St James's Hospital, vitamin D deficiency has reached epidemic proportions globally, with more than one billion people thought to be affected.

Currently, the best way to assess vitamin D levels is via a blood test. However, this requires expertise and training, along with hygienic conditions and equipment, and it can be painful for the patient.

Furthermore, a blood test only provides the vitamin D status at a single point in time, however vitamin D changes with the season. A person can have sufficient levels in the summer, but be deficient in the winter.

This latest study is the first in the world to report that it is possible to extract and measure vitamin D in human hair. Furthermore, because hair grows around 1cm per month, this could show vitamin D status over a number of months, allowing the large seasonal differences to be captured.

"This study presents the first step towards the development of a novel test for assessing vitamin D status over time. The idea is that vitamin D is being deposited continuously in the hair as it grows; more might be deposited at times when vitamin D concentration in the blood is high, and less when it's low.

"Therefore, a test based on the hair sample might be able to give doctors a measure of vitamin D status over time - if hair is long enough, this even might be over a few years," explained the study's lead author, associate professor Lina Zgaga of TCD.

She said that more research is needed to establish the exact link between vitamin D concentration in the blood and in the hair over time.

"We also need to investigate different factors that might affect vitamin D levels in hair, the most obvious ones being hair colour and thickness, or use of hair products such as hair dye," she noted.

According to the study's co-author, Dr Martin Healy of St James's Hospital, the presence of vitamin D in the hair ‘could be interpreted as a personal record of a person's vitamin D status'.

"Having a knowledge of an individual's long-term vitamin D status through analysis of hair samples may allow for better strategies to maintain stable and adequate vitamin D concentrations over an extended period.

"The finding that vitamin D can be measured in hair samples potentially opens up a new approach to epidemiological studies relating the vitamin to bone and non-bone related medical conditions, which have been associated with its deficiency," he commented.

Meanwhile, according to the study's co-author, Dr Eamon Laird of TCD, this discovery could also be used to give a clearer picture of history.

"Other applications could also include historical samples from archaeological sites. Hair (along with teeth) are some of the longest lasting surviving biological materials after death and thus it could be possible to for the first time assess the vitamin D status of historical populations - Elizabethans, Viking, Celtic, Roman, ancient Chinese, Egyptian.

"Similarly, hair samples could also be used to assess longer-term vitamin D status in animals, with applications to farming," he said.

Details of these findings are published in the international nutrition journal, Nutrients.