阳光照射会影响肠道细菌

阳光照射会影响肠道细菌

People living at higher latitudes may be safer from the dangers of too much sunlight, but they also face a greater risk of having too little vitamin D in their bodies, a deficiency that affects as many as 1 billion people around the world.

生活在高纬度地区的人们可能更安全，免受过多阳光的危害，但他们也面临着体内维生素D太少的更大风险，这一缺陷影响着全世界多达10亿人。

For the first time, scientists have directly linked sun exposure to changes in the gut microbiome. (Photo: Kanchana P/Shutterstock)

A vitamin D deficiency alone can lead to a variety of health problems. Along with other environmental factors like diet and antibiotic use, it's also seen as one reason why many developed countries have such high rates of chronic inflammatory diseases, including multiple sclerosis and inflammatory bowel disease (IBD).

单单缺乏维生素D就会导致各种健康问题。除了饮食和抗生素使用等其他环境因素外，它也被视为许多发达国家患有慢性炎症疾病(包括多发性硬化症和炎症性肠病(IBD))的原因之一。

Research suggests our gut microbiomes — the bacteria and other tiny creatures living in our digestive tracts — might wield some influence over these conditions. And now, in a study published in the journal Frontiers in Microbiology, researchers reveal a potentially important way to boost our gut bacteria with sunlight.

研究表明，我们的肠道微生物群——生活在我们消化道中的细菌和其他微小生物——可能会对这些情况产生一些影响。现在，在一项发表在《微生物学前沿》杂志上的研究中，研究人员揭示了一种利用阳光促进肠道细菌生长的潜在重要方式。

A 'novel skin-gut axis'

一个“新的皮肤-内脏轴”

Even briefly shining ultraviolet B (UVB) light onto a person's skin can lead to a wider diversity of gut bacteria, the researchers found, as well as higher levels of vitamin D. This was a small study, and the effect was only seen in subjects with lower vitamin D levels. Still, this is the first study to find a direct effect from UVB light on the gut microbiome, the researchers write, suggesting "the existence of a novel skin-gut axis that could be used to promote intestinal homeostasis and health."

研究人员发现，即使只是短暂地将紫外线B照射在人的皮肤上，也会导致肠道细菌的多样性增加，维生素D的含量也会增加。不过，研究人员写道，这是首次发现UVB光对肠道微生物群有直接影响的研究，表明“存在一种新的皮肤-肠道轴，可以用来促进肠道内环境平衡和健康。”

There are two basic types of ultraviolet light that reach Earth's surface, known as UVA and UVB. Both can be harmful, but UVB rays are the main rays responsible for sunburns and are thought to cause the most skin cancers, according to the American Cancer Society. At the same time, UVB rays from sunlight trigger our bodies to produce vitamin D. Low UVB exposure has been linked to the onset of inflammatory gut diseases, and since vitamin D can influence our gut bacteria, the researchers hoped to shed new light on the relationship among all three factors.

到达地球表面的紫外线有两种基本类型，即UVA和UVB。这两种射线都是有害的，但据美国癌症协会称，UVB是造成晒伤的主要射线，被认为是导致皮肤癌的主要原因。同时,从太阳光UVB引发人体产生维生素D低UVB照射与炎性肠道疾病的发病有关,因为维生素D可以影响我们的肠道细菌,研究人员希望揭示所有三个因素之间的关系。

Levels of UV light from the sun tend to be naturally lower at higher latitudes, raising the risk of health problems from a vitamin D deficiency. (Photo: yanikap/Shutterstock)

Led by Else Bosman, a doctoral candidate in experimental medicine at the University of British Columbia, the researchers recruited 21 healthy women to participate in the study. All of the volunteers had fair skin and lived in Canada during winter for the three previous months, and thus were exposed to relatively low levels of UVB light. Before the study began, the researchers tested their vitamin D levels and took stool samples, which revealed the makeup of their gut microbiome.

在不列颠哥伦比亚大学实验医学博士生爱尔莎·博斯曼的带领下，研究人员招募了21名健康女性参与研究。所有的志愿者都是白皮肤，前三个月都住在加拿大的冬季，因此暴露在相对较低水平的UVB光线下。在研究开始之前，研究人员测试了他们的维生素D水平，并采集了粪便样本，这些样本揭示了他们肠道菌群的组成。

Nine of the women had been taking vitamin D supplements for three months prior to the study, while 12 hadn't. Of those 12, most had insufficient levels of vitamin D. The researchers gave the volunteers three sessions of UVB light exposure in a week, then tested their vitamin D and stool again. Not only did the women with low vitamin D now have normal levels, but their gut microbiomes had also grown more diverse.

在研究之前，其中9名女性已经服用了3个月的维生素D补充剂，12名没有服用。在这12名志愿者中，大多数人体内的维生素D含量不足。研究人员让志愿者在一周内接受三次紫外线照射，然后再次测试他们的维生素D和粪便。维生素D含量低的女性不仅体内的维生素D含量正常，而且肠道菌群也变得更加多样化。

More research needed

需要更多的研究

This study was small, and its findings are still "extremely preliminary," as Leslie Nemo writes for Discover Magazine. More research will be needed before we can draw firm conclusions or take action based on these findings. It's especially important to be careful with sunlight exposure given the potential risks, and the researchers note they didn't use actual sunlight in this study, just an isolated component of it.

正如莱斯利·尼莫为《发现》杂志所写的那样，这项研究的规模很小，其发现也“极其初步”。在我们得出确切的结论或根据这些发现采取行动之前，还需要进行更多的研究。考虑到潜在的风险，在阳光照射下要格外小心，这一点尤其重要。研究人员指出，他们在这项研究中并没有使用实际的阳光，只是其中一个孤立的成分。

Still, this study fills in some blanks and offers intriguing hints in our quest to understand the human microbiome, showing a shift in gut bacteria that was apparently driven mainly by the body's production of vitamin D.

尽管如此，这项研究填补了一些空白，为我们探索人类微生物群落提供了有趣的线索，显示肠道细菌的变化显然主要是由人体维生素D的生产驱动的。

"It is well known that UVB light produces vitamin D, and we now start to understand that vitamin D is important to maintain a healthy gut," Bosman says. While those facts were known individually, she adds, this is the first study linking them all together. This study should now be repeated with more volunteers, the researchers say, including both sexes and a wider range of skin types.

“众所周知，UVB光会产生维生素D，现在我们开始明白维生素D对保持肠道健康很重要，”博斯曼说。她补充说，虽然这些事实是单独知道的，但这是第一次把它们联系在一起的研究。研究人员说，这项研究现在应该在更多的志愿者身上重复进行，包括男性和女性，以及更广泛的皮肤类型。