Scientists can tell how much sun you have been exposed to – by looking at your FAECES

Scientists now say they can tell how much sun you have been exposed to – by looking at your faeces.

In the first study of its kind, researchers investigated how exposure to UVB light alters gut bacteria.

By looking at stool samples, they found women who went in a sunbed for three minutes a week benefited from a boost of good bugs.

It is likely vitamin D, produced by our bodies when skin is exposed to sunlight, is responsible for restoring a healthy gut balance.

Scientists said the findings are ‘exciting’ because they explain how light therapy could be useful for conditions such as inflammatory bowel disease (IBD), which may be triggered by an unbalanced gut.

Researchers at The University of British Columbia investigated how exposure to UVB light alters gut bacteria, finding it boosts good bugs

In the study, published in the journal Frontiers in Microbiology, 21 healthy women from Vancouver were recruited by the University of British Columbia.

Nine had taken vitamin D supplements over the past three months. Twelve of them had not, however.

Before and after treatment, stool samples were taken to analyse their gut bacteria, as well blood samples to check vitamin D levels.

The supplement group had sufficient levels of vitamin D while the remaining 12 did not.

The latter had ‘significantly lower diversity and richness’ in their gut at the beginning of the study.

WHAT ARE THE RISKS OF VITAMIN D DEFICIENCY?

Vitamin D deficiency – when the level of vitamin D in your body is too low – can cause your bones to become thin, brittle or misshapen.

Vitamin D also appears to play a role in insulin resistance, high blood pressure and immune function – and this relates to heart disease and cancer – but this is still being investigated.

Low levels of the vitamin have also long been linked to an increased risk of multiple sclerosis.

Although the amount of vitamin D adults get from their diets is often less than what’s recommended, exposure to sunlight can make up for the difference.

For most adults, vitamin D deficiency is not a concern.

However, some groups – particularly people who are obese, who have dark skin and who are older than age 65 – may have lower levels of vitamin D due to their diets, little sun exposure or other factors.

Source: Mayo Clinic

All the participants had three one-minute sessions in a full-body sunbed in a single week.

Exposure to UVB in sunlight drives production of the so-called ‘sunshine vitamin’ in the skin.

Participants had an average increase in vitamin D levels of ten per cent, according to the findings.

However, only those not taking vitamin D supplements had increased gut microbial diversity after the UVB exposure.

Improvements resulted in a similar gut diversity to those who had been taking a supplement.

Professor Bruce Vallance, who led the study, said: ‘Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements.

‘UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.’

The study suggests that vitamin D mediates the change in gut bacteria.

The largest effect was an increase in the abundance of Lachnospiraceae bacteria after the UVB light exposures.

Professor Vallance, who called the findings ‘exciting’, said: ‘Previous studies have linked Lachnospiraceae abundance to host vitamin D status.

‘We too found a correlation with blood vitamin D levels, which increased following UVB exposure.’

The results also showed some agreement with mouse studies using UVB, such as an increase in Firmicutes and decrease in Bacteroidetes in the gut following exposure.

The study is not designed to show the exact mechanism by which the microbiome changes occur.

Both UVB and vitamin D are known to influence the immune system, ‘which in turn affects how favorable the intestinal environment is for the different bacteria’, suggests Professor Vallance.

He added: ‘The results of this study have implications for people who are undergoing UVB phototherapy, and identifies a novel skin-gut axis that may contribute to the protective role of UVB light exposure in inflammatory diseases like MS and IBD.’

Sun exposure, vitamin D levels and the gut bacteria have each been linked to inflammatory conditions such as multiple sclerosis and IBD.

Recent studies suggest vitamin D alters the human gut microbiome, giving weight to the ‘skin-gut-axis’ theory.

Until now, the theory that UVB causes gut microbiome changes, through vitamin D production, had only been shown only in rodents.

However, Nikul Bakshi, research programme lead at Crohn’s & Colitis UK, stressed the study did not look at patients with IBD.

He said: ‘This study is looking at the link between vitamin D and the gut microbiome, and not the impact of vitamin D on Crohn’s and colitis directly.’

Low levels of vitamin D and good gut bacteria have also long been linked to an increased risk of multiple sclerosis.

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