"/>

Does Vitamin D Protect Against COVID-19?

杰西卡·麦克唐纳(Jessica McDonald)

问:维生素D是否有助于预防COVID-19?

答:一些科学家认为维生素D可能有帮助,但是没有直接证据表明维生素D可以预防COVID-19或减轻疾病的严重程度。但是,它应该成为健康生活方式的一部分。

完整问题

维生素D可以帮助减少covid 19的机会吗?

完整答案

随着冠状病毒在全球范围内传播,一些科学家提出维生素D可以帮助治疗由病毒引起的疾病COVID-19。 

例如,前疾病控制与预防中心主任汤姆·弗里登(Tom Frieden)博士在3月23日 在福克斯新闻网站上发表了  专栏文章,暗示维生素D可以降低人的COVID-19风险。

他认为:“有很多关于奇迹疗法的浮躁表达式,但科学支持(虽然不是证据)维生素D可能增强免疫系统的可能性,尤其是维生素D水平低的人的免疫力。”

这个想法部分源于一些实验,这些实验发现,阳光照射后在皮肤中合成的维生素可以 在免疫系统中使用,这种维生素可以在某些食物中找到  一些  研究  还表明,维生素D补充剂可能会预防呼吸道感染,特别是如果有人缺乏维生素。许多受冠状病毒影响最大的人,例如老年人和少数族裔,经常维生素D水平升高。

但是专家提醒不要过度解释初步的相关性或假设机制最初的州立大学  营养学家  A. 凯瑟琳·罗斯告诉我们的,关联与因果关系并不相同,支持或反对维生素D和COVID-19的证据“极其”。薄弱”。

一个  快速的回顾  ,从牛津大学的中心循证医学发现“没有临床证据”,维生素d能预防或治疗COVID-19,另一个  审查  通过近两打的营养学专家发表主题  BMJ营养,预防和健康  建议避免维生素D缺乏症,但警告不要服用高剂量的维生素。

作者认为:“作为一种重要的微量营养素,应特别关注维生素D,而不是作为击败COVID-19的’灵丹妙药”,因为目前科学证据的基础非常缺乏,而应将维生素D作为维生素D的一部分。健康的生活方式策略,以确保人们在最佳最佳的地方获得营养。”

因此,除非获得足够的维生素D(无论是否大流行)是一个好主意,但现在说维生素D的缺乏使COVID-19变得更糟,或者补充维生素D可以预防这种疾病还为时过早。 

维生素D基础

维生素D虽然被称为维生素,但它在体内却起着激素的作用,并以增强骨骼而闻名,这在很大程度上是通过促进   体内中钙和磷的吸收来实现的。

“这实际上是一种激素,在我们拥有的所有营养素中,它是唯一的非饮食来源的营养素,” 英国萨里大学维生素D专家Susan Lanham- Newsay 。 

相反,她告诉我们,大多数人的维生素d是在皮肤暴露在阳光下,这就是为什么深色皮肤的人做  更容易  有维生素水平升高,为什么人谁去外面那么交替,包括那些年龄严重或健康状况较差的人容易出现缺陷。

对于要被人体使用维生素d,必须将其转化为活性形式,通常由肝和肾,美国根据国立卫生研究院一个  事实这种营养素仅在几种食物中天然存在,例如鸡蛋和油性鱼,但在美国,这种营养素在包括牛奶和谷类内部的经过强化的食品中得到了广泛的应用。

尽管人们 对到底需要多少维生素d以及缺乏维生素问题存在  争议,但兰哈姆-新表示,缺乏维生素的常用标准是每升血液中的血液水平低于25-30纳摩尔维生素d 含量过少会  导致  儿童病或成人骨软化症-骨骼变软并变形的情况。 

但是,维生素D可以脂溶并存于体内,因此,添加更多并不一定总能带来好处。Lanham -Newsay:“如果过多的维生素D,您会得到所谓的高钙血症,”这是指血液中钙的含量升高   ,这对高血压疾病的人来说尤其是危险。

维生素D和免疫力

除了在骨骼健康中的作用外,维生素D还可以在免疫系统中发挥作用,这是某些人认为营养物可能影响COVID-19的关键原因。

例如,Lanham-Newsay,免疫细胞上存在维生素D受体,一些免疫细胞产生的酶可以帮助将营养转化为活性形式。

她说:“这为维生素D在维持免疫系统中的潜在作用提供了科学依据。”

培养在细胞中进行的 一些实验  表明  ,维生素d触发可以包括  肺细胞在内的抗菌肽的产生,抗菌肽这些  可能起到抵抗入侵病原体的作用英文。

其他实验室实验发现,  维生素D可能通过那些反应偏向向少数发炎的反应(包括  减少  某些促炎性细胞因子或信号蛋白的产生)来抑制过度活跃的免疫反应  。 

一些研究人员  假设  这种机制可能与冠状病毒有关,因为一些COVID-19患者经历了威胁生命的细胞因子激增,称为  细胞因子风暴  ,随着免疫细胞涌入肺部清除病毒,可破坏器官。

但是,尽管许多基础研究表明维生素D在免疫系统中起作用,但尚不清楚这些机制是否适用于临床实践。评估维生素D是否可以治疗或预防传染病的研究通常   不一致的

有证据表明维生素D可以预防呼吸道感染。2017年,伦敦玛丽皇后大学的研究人员在《医学   杂志》(BMJ)  上发表了荟萃分析  ,汇总了25项随机对照试验的个体患者数据,这些试验对补充维生素D的各种疾病进行了测试,  包括  流感,肺炎,感冒和耳部感染。 

The authors identified a protective effect for those taking vitamin D supplements daily or weekly, with the greatest benefit going to those who had the lowest levels of the vitamin to start. Periodic large doses, or boluses, of vitamin D were not effective.

An accompanying editorial, however, noted that the absolute risk of coming down with at least one respiratory infection when taking vitamin D supplements dropped by only 2 percentage points — from 42% to 40% — and that given differences between the studies that were analyzed, large randomized controlled trials were still needed.

Lack of Evidence for Vitamin D and COVID-19

Because the coronavirus is so new, little rigorous research has been done specifically on vitamin D and COVID-19.

Oxford’s rapid review, which was posted last month and reflected literature searches performed in April, did not identify any clinical evidence that vitamin D is beneficial for COVID-19. The report concluded that “well-masked randomized trials” were needed before specifically recommending the nutrient for COVID-19, but that Britons should already be taking vitamin D supplements anyway, per national guidance. 

Since then, a variety of published and unpublished studies investigating potential links between vitamin D and COVID-19 have appeared, but Dr. Joseph Lee, a general practitioner and co-author of the report, told us that he was not aware of any subsequent studies that would alter his group’s recommendation that “people should take vitamin D, but not because of COVID-19.”

Lanham-New, who was the lead author of the BMJ Nutrition, Prevention & Health review, also said her conclusions had not changed.

One U.K. study, published on May 6 in Aging Clinical and Experimental Research, identified a crude association between the average vitamin D level reported in 20 European countries and the number of per-capita COVID-19 cases and deaths in those nations. 

Another similar paper, appearing in the Irish Medical Journal, found an inverse relationship between the vitamin D levels in older people in different European countries, as reported in past studies, and a country’s COVID-19 mortality rate, with fish-loving Nordic countries generally faring better than those in southern Europe.

But these so-called ecological epidemiology studies can only hint at any effect of vitamin D, since they’re simple correlations at the population level. “This is not a design suited to identifying causal effects,” Lee said, “and I would not consider them as evidence of a role for vitamin D in COVID-19.”

Other reports also claim to identify links between lower levels of vitamin D and COVID-19 infection or disease severity in different cohorts of people, but most of these have not yet been vetted by other scientists through peer review. 

One unpublished report of 780 confirmed COVID-19 cases in Indonesia found that the majority of deaths occurred in patients with abnormally low vitamin D blood levels, and claimed to have found an association between vitamin D deficiency and COVID-19 mortality after controlling for other factors, such as other preexisting health conditions.

But as Lanham-New noted in an interview, the paper “doesn’t in any way prove cause and effect.” Lee, too, said that while the authors attempted to control for other health conditions, the group did so in an odd way, lumping all of the conditions together. And even if the team had controlled for them individually, that doesn’t necessarily eliminate bias, so the relationship could reflect the fact that people who are in poorer health generally fare worse with COVID-19.

“It is relatively easy to calculate associations, and that is what most of these papers have done,” Penn State’s Ross said. “But associations do not show cause and effect, and in fact, ‘reverse causation’ is not carefully considered.” The disease itself could cause a reduction in a person’s vitamin D levels, she said, noting that there are negative associations of serum vitamin D with diabetes, obesity and other infections. “I place little confidence on any of these studies,” she said.

More credible, Ross said, were two analyses of U.K. biobank data, neither of which support the idea that less vitamin D leads to a higher risk of COVID-19 infection. Given concerns that the disproportionate number of coronavirus infections in blacks and South Asians in the U.K. could be due to lower vitamin D levels in darker-skinned people, the researchers checked to see if there was any connection between a person’s vitamin D levels, which had been measured in participants about a decade ago, and testing positive for COVID-19.

While the published report affirmed that black and South Asian participants were several times more likely to test positive for COVID-19 than whites, there was no association with vitamin D. The authors concluded that vitamin D “is unlikely to be the underlying mechanism for the higher risk observed in black and minority ethnic individuals and vitamin D supplements are unlikely to provide an effective intervention.”

The other analysis, which Lanham-New said has since been submitted to a journal with additional participant data, found no difference in vitamin D status among those who tested positive versus negative for COVID-19. She said additional work was planned once COVID-19 severity and mortality data became available.

Another consideration when interpreting many observational studies, Lee said, is something called collider bias, which can sometimes result in spurious correlations when the people included in a dataset aren’t representative of the wider population. Some researchers have already noted that COVID-19 studies may be especially prone to collider bias, making it hard to identify risk factors and medications that work.

Consider a study analyzing outcomes among people who are tested for COVID-19. Some people are likely getting tested because they are quite ill and have been admitted to the hospital, while others may be tested because they’re a health care worker or because they’re more privileged and have access to testing.

In this scenario, Lee said, people with good levels of vitamin D will be less likely to test positive, compared to the sick people. “This selection will in itself induce an association between low vitamin D and COVID-19 positive tests or severity of disease,” he said, “even if it isn’t true in the general population.”

Recommendations

In the end, Ross is skeptical that vitamin D will prove to be beneficial for COVID-19, although she hesitated to entirely discount the possibility, given how much is still unknown about the disease.

“[I]t is hard for me to conceive that vitamin D has much chance of being as effective as other kinds of treatments, if at all,” she said. “We don’t know however.”

Several randomized controlled trials are in the works, which may reveal a more concrete answer.

Her recommendation, irrespective of COVID-19, is to consume vitamin D-rich foods or take a supplement to provide the recommended dietary amount, or RDA, of 600-800 International Units per day. This matches the Institute of Medicine’s national guideline, which Ross helped write, and which assumes minimal sun exposure.

One cup of fortified milk, for example, contains 120 IUs of vitamin D, while a 3-ounce serving of cooked salmon provides 570 IUs.

Lanham-New emphasized that excessive doses of vitamin D should not be used. But especially for those who have been cooped up indoors while social distancing, it may be a good idea to take regular supplements. 

“If you’re in self-isolation, definitely be taking a vitamin D supplement according to your government guidelines,” she said. 

Lee also pointed to following state or national vitamin D recommendations. “There is no reason to think it will help with COVID-19, but that might change when the trials report,” he said of vitamin D. “Our advice is to take vitamin D in accordance with local guidelines.”

Editor’s note: FactCheck.org does not accept advertising. We rely on grants and individual donations from people like you. Please consider a donation. Credit card donations may be made through our “Donate” page. If you prefer to give by check, send to: FactCheck.org, Annenberg Public Policy Center, 202 S. 36th St., Philadelphia, PA 19104.

Sources

Frieden, Tom. “Former CDC Chief Dr. Tom Frieden: Coronavirus infection risk may be reduced by Vitamin D.” Fox News. 23 March 2020.

Vitamin D: Fact Sheet for Consumers.” NIH. Accessed 5 June 2020.

Martineau, Adrian R., et. al. “Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.” BMJ. Vol. 356 (2017).

Ross, A. Catharine. Professor of Nutrition and Physiology, Pennsylvania State University. Emails to FactCheck.org. 3 and 5 June 2020.

Lee, Joseph, et. al. “Vitamin D: A rapid review of the evidence for treatment or prevention in COVID-19.” 1 May 2020.

Johnson, Larry E. “Vitamin D Deficiency.” Merck Manual Consumer Version. Accessed 5 June 2020.

Lanham-New, Susan A., et. al. “Vitamin D and SARS-CoV-2 virus/COVID-19 disease.” BMJ Nutrition, Prevention & Health. 13 May 2020.

Lanham-New, Susan. Head of the Department of Nutritional Sciences, University of Surrey. Interview with FactCheck.org. 5 June 2020.

Bischoff-Ferrari, Heike and Walter Willett. “Comment on the IOM Vitamin D and Calcium Recommendations.” The Nutrition Source, Harvard T.H. Chan School of Public Health. 25 Dec 2010. 

Vitamin D: Fact Sheet for Health Professionals.” NIH. Accessed 5 June 2020.

Kearns, Malcolm D., et. al. “Impact of vitamin D on infectious disease.” American Journal of the Medical Sciences. Vol. 349. Issue 3 (2015).

Liu, Philip T., et al. “Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response.” Science. Vol. 311. (2006).

Hansdottir, Sif, et. al. “Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense.” Journal of Immunology. Vol. 181. Issue 10 (2008).

Olliver, Marie, et. al. “Immunomodulatory Effects of Vitamin D on Innate and Adaptive Immune Responses to Streptococcus pneumoniae.” The Journal of Infectious Diseases. Volume 208. Issue 9 (2013).

Zhang, Yong, et. al. “Vitamin D inhibits monocyte/macrophage proinflammatory cytokine production by targeting MAPK phosphatase-1.” Journal of immunology. Vol. 188. Issue 5 (2012).

Laird, E., et. al. “Vitamin D and Inflammation: Potential Implications for Severity of Covid-19.” Irish Medical Journal. Vol. 113. Issue 113 (2020).

Cytokine storm.” NCI Dictionary of Cancer Terms. Accessed 5 June 2020.

Wu, Dayong, et. al. “Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance.” Frontiers in Immunology. Vol. 9. Issue 3160 (2019).

Bolland,Mark J.和Alison Avenell。维生素D补充剂是否有助于预防呼吸道感染?” BMJ。356(2017)。

电子邮件至FactCheck.org。电子邮件FactCheck.org。2020年6月3日至4日。李,约瑟夫。牛津大学纳菲尔德初级保健健康科学系全科医生和博士医师

Ilie,Petre Cristian等。维生素D在预防冠状病毒疾病2019年感染和死亡中的作用。” 老化的临床和实验研究。2020年5月6日。

Meltzer,David O.等。维生素D缺乏症与治疗与COVID-19发病率的关联。” medRxiv。2020年5月13日。

补充维生素D可能会改善感染冠状病毒-2019(COVID-19)的患者的临床结果。” SSRN。2020年4月9日。阿里皮奥,马克

Raharusun,普拉博沃等。COVID-19死亡率和维生素d的模式:印度尼西亚的研究。” SSRN。2020年4月26日。

Hastie,Claire E等。英国生物库中的维生素D浓度和COVID-19感染。” 糖尿病与代谢综合症,第一卷14,4 561-565。2020年5月7日

达令(达林),安德里亚(安德烈L.)等。维生素d的状态,体重指数,种族和COVID-19:对首次报告的英国生物库COVID-19阳性病例(580例)与阴性对照(723例)的初步分析。” medRxiv。2020年5月5日。

对撞机偏见。” 牛津大学循证医学研究中心偏见目录。于2020年6月5日访问。 

2020年夏普,杰玛和蒂姆·莫里斯。对撞机偏见:为什么很难找到COVID-19感染及其严重程度的危险因素或有效药物。” 尤里卡!博客,布里斯托大学5月10日。

Give a Comment