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As we move into warmer months, the words ‘I’m going to go out for some Vitamin D’ are beginning to make their appearance in conversation. Vitamin D is essential for bone growth, and plays an important role in immunity and muscle function, yet most of the vitamin that our bodies absorb comes from sunlight. In the UK, where the sun often feels a rare pleasure, around half of the population are estimated to have below-optimal Vitamin D levels. Given the increased availability of supplements and treatments, you might assume that we have better access to our necessary quota than past populations – but is this true?
The most common method for assessing Vitamin D levels is through blood analysis, which is of course not feasible when assessing archaeological human remains. Instead, a person’s Vitamin D status is usually inferred by looking for evidence of deficiency that is manifested in the skeleton, such as dental issues, or conditions like rickets or osteomalacia. While these indicators can signpost a clear vitamin deficiency, however, they don’t allow for an empirical estimate of Vitamin D status, and those with only minor deficiencies are harder to identify.
Recent studies focused on modern individuals may offer an alternative, using cut hair samples to analyse Vitamin D levels. This method is simpler, less invasive, and more economical than research using blood – and, unlike blood, hair is known to survive in some archaeological contexts. A new study from the University of Aberdeen, published in Nature Scientific Reports, has set out to investigate this potential. Researchers took samples of cut hair from 16 modern Scottish participants, as well as one archaeological individual whose remains had been recovered during excavations by Aberdeen City Council Archaeological Unit at St Nicholas Kirk, Aberdeen, in 2006.
This site has produced an impressive skeletal assemblage spanning the 12th to 18th centuries (see CA 258), and some of the individuals have previously been used in several diachronic population studies, including examinations of breastfeeding practices (Britton et al., 2018, ‘Isotopes and new norms: investigating the emergence of early modern UK breastfeeding practices at St Nicholas Kirk, Aberdeen’, International Journal of Osteoarchaeology 28: 510-522), and adult diet and mobility (Czére, 2020, From the Dark Ages to the Medieval State: a diachronic isotopic study of dietary change in Scotland, from the Early to the High Medieval Period, PhD thesis: University of Aberdeen, and also in an unpublished study by Kate Britton). The human remains that featured in the University of Aberdeen’s Vitamin D study are believed to represent a man aged 25-29 who had been buried in the post- medieval phase of the church cemetery. Crucially, strands of hair were still attached to his skull, allowing the researchers to compare his Vitamin D levels to those of the modern participants, in the first study of its type.
The hair samples were taken close to the root, aligned by the cut end, and sliced into sequential segments to minimise the necessary sample size. Each sample was then analysed, and the concentrations of 25(OH)D3 (a metabolite also known as calcifediol or calcidiol) measured. A person’s 25(OH)D3 level, as measured in a serum or plasma, is a naturally occurring marker that reflects diet, as well as the body’s production of Vitamin D in response to UVB radiation. Out of the modern samples, 14 of the 16 participants had levels of 25(OH)D3 that were detectable from their hair samples. The median Vitamin D measurement of the three modern individuals with the highest levels was 38,442.0 picograms per milligram; two reported taking vitamin supplements. However, the majority of participants had much lower levels of Vitamin D, with the average falling well below 10,000pg/mg.
Interestingly, while you might expect – given the availability of supplements today and the presumably vastly different dietary and lifestyle choices between the post-medieval period and the present – that the modern and archaeological individuals would have shown very different Vitamin D levels, this was not the case. The hair sample taken from the St Nicholas Kirk skeleton was found to have Vitamin D concentrations of 342.6 to 2254.6pg/mg (it varied dependent on the position of the tested segment along the 17cm-long hair strand). This falls within the same range as the majority of the modern participants, suggesting that Vitamin D levels in medieval Aberdeen were similar to those today.
The study conducted stable isotope analysis on the archaeological sample, too, to explore what other factors affecting Vitamin D levels may have been at play. By examining samples taken from down the length of the lock of hair, changes in levels of elements such as oxygen, hydrogen, carbon, nitrogen, and sulphur over the length of time that the hair had grown could be determined. This revealed that the levels of Vitamin D may have correlated with increased sun exposure in warmer months, as well as an increased consumption of fish in the summer before the man’s death.
While the researchers recognise that the study was limited in terms of sample size, the results reflect promising potential for further use of segmental hair analysis as a non-invasive test for Vitamin D levels in both a modern medical context, or when analysing data from past populations. The full study is available online at http://www.nature.com/articles/s41598-025-86097-6 (open access).
Text: Rebecca Preedy / Image: N Chadwick (CC BY-SA 2.0)
