Winter is upon us and so is the risk of vitamin D deficiency and infections. Vitamin D, which is made in our skin following sunlight exposure and also found in oily fish (mackerel, tuna and sardines), mushrooms and fortified dairy and nondairy substitutes, is essential for good health. Humans need vitamin D to keep healthy and to fight infections. The irony is that in winter, when people need vitamin D the most, most of us are not getting enough. So how much should we take? Should we take supplements? How do we get more? And, who needs it most?
Where to Get Your Vitamin D<p>Vitamin D is called the sunshine vitamin since it is made in the skin after exposure to sun. The same UVB rays that cause a sunburn also make vitamin D. Sunscreen, darker skin pigmentation, clothing and reduced daylight in winter diminish the skin's ability to make vitamin D. The people who experience the biggest seasonal swings in vitamin D levels are fair-skinned individuals <a href="https://doi.org/10.3390/nu10040457" target="_blank">living in the northern regions</a> of the U.S. and at <a href="https://doi.org/10.3945/an.117.015578" target="_blank">higher latitudes around the globe</a> where there is very little daylight in winter.</p><p>But those most at risk for low vitamin D levels are people of color and people living at higher latitudes. Dark-skinned individuals are more likely than fair-skinned individuals to be low for vitamin D year-round because the darker skin blocks the UVB rays from producing vitamin D. However, even in dark skinned individuals, vitamin D is lowest in the winter.</p><p>In the winter, in addition to high vitamin D food, adults should take additional vitamin D from foods and/or supplements to <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#en1" target="_blank">get at least 600 IU per day of vitamin D.</a> People who have dark skin or avoid sunshine should eat more vitamin D year-round.</p>
Vitamin D's Importance for Bones and Microbes<p>Originally, doctors thought that vitamin D was only important for bone health. This was because the vitamin D deficiency caused bone diseases like <a href="http://doi.org/10.1172/JCI29449" target="_blank">rickets in children and osteoporosis in adults</a>. However, in the 1980s scientists discovered that <a href="https://www.jci.org/articles/view/111557" target="_blank">immune cells</a> <a href="https://science.sciencemag.org/content/224/4656/1438" target="_blank">had receptors for vitamin D</a>.</p><p>My group's research has shown that vitamin D plays an important role in <a href="https://doi.org/10.1080/10409238.2019.1611734" target="_blank">maintaining health in the gastrointestinal tract</a>. <a href="https://iai.asm.org/content/84/11/3094" target="_blank">Higher levels of vitamin D</a> reduce <a href="https://doi.org/10.1016/j.tem.2019.04.005" target="_blank">susceptibility to inflammatory bowel disease</a> and <a href="http://doi.org/10.1038/ajg.2016.53" target="_blank">Crohn's disease</a>, <a href="https://doi.org/10.3389/fimmu.2019.00001" target="_blank">gut</a> and <a href="http://doi.org/10.1128/IAI.00679-16" target="_blank">lung infections</a> in animals and people.</p><p>My colleagues and I have discovered that one of the ways vitamin D functions is by keeping the microbes in the gut healthy and happy. Vitamin D <a href="https://doi.org/10.1177/1535370214523890" target="_blank">increases the number and diversity of microbes</a> living in the gut, which together reduce inflammation throughout the body.</p><p>Low vitamin D levels are <a href="https://doi.org/10.1038/nrgastro.2015.34" target="_blank">associated with inflammatory bowel disease</a> in humans. Researchers have found that <a href="https://doi.org/10.1007%2Fs00535-017-1313-6" target="_blank">inflammatory bowel disease patients in Japan</a> have more symptoms in winter than during other seasons.</p>
Why is vitamin D more important in winter?<p>In the winter, humans are exposed to more infections and spend less time outside. Exactly how much vitamin D healthy adults should have is debated. Some authorities recommend from <a href="https://www.nature.com/articles/nrendo.2017.31" target="_blank">200 IU per day to 2,000 IU per day</a>. In the U.S., the <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">Institutes of Medicine</a> recommends 600-800 IU per day for adults, while the <a href="https://doi.org/10.1210/jcem.96.12.zeg3908" target="_blank">Endocrine Society states that optimal vitamin D status</a> may require 1500-2,000 IU per day. In the winter, people have a reduced ability to make vitamin D when they go outside, so amounts of at least 600 IU per day of vitamin D from food or supplements would help maintain vitamin D status at summer levels.</p><p>But, just like many things, <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">too much vitamin D can be harmful</a>. Vitamin D toxicity does not result from too much sun or food. Because of the risk of skin cancer, dermatologists and other health professionals do not recommend unprotected sun exposure to boost your vitamin D. Instead they suggest supplements. But vitamin D toxicity can occur if an individual takes too many.</p><p>The experts that set the national intakes of vitamin D for the U.S. recommend that adult individuals take <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">no more than 4,000 IU per day of vitamin D</a> to avoid toxic side effects. Vitamin D helps you absorb calcium from your diet, but when vitamin D is too high, calcium levels in the blood go up and that can lead to kidney disease.</p><p>By consuming more vitamin D during the winter your gut microbes will be healthier and you'll be more resistant to infection and inflammation year-round.</p>
EcoWatch Daily Newsletter
This story is a roundup of articles from The Conversation's archives.
As cold weather settles in across North America, some communities have already started up their snowplows, while others keep watchful eyes on the forecast. Snow and ice can wreck travel plans, but they also play important ecological roles. And frozen water can take amazing forms. For days when all talk turns to winter weather, we spotlight these five stories from our archives.
1. The Strange Forms Water Can Take<p>Beyond snowflakes and icicles, <a href="https://theconversation.com/steaming-lakes-and-thundersnow-4-questions-answered-about-weird-winter-weather-110936" target="_blank">frozen water can behave in surprising ways</a>. For example, during very cold snaps, lakes can appear to steam like a sauna bath.</p><p>As Colorado State University atmospheric scientist <a href="https://scholar.google.com/citations?user=M8R-NhQAAAAJ&hl=en" target="_blank">Scott Denning</a> explains, this happens because the liquid water in the lake can't be colder than the freezing point — about 32 degrees Fahrenheit. As water evaporates from the relatively warm lake into the cold dry air, it condenses from vapor (gaseous water) to tiny droplets of water in the air, which look like steam.</p><p>When it gets extremely cold, ice can form on the ocean's surface. Waves break it up, so the water starts to look like an undulating slurpee. "For anyone willing to brave the cold, it's wild to stand by the shore and watch the smoking slushy sea with its slow-motion surf," Denning writes.</p>
2. How Road Salt Tames Ice<p>When a big storm is forecast, utility trucks often will head out to pre-treat streets and highways, typically spraying rock salt or saltwater solutions. But contrary to popular belief, <a href="https://theconversation.com/salt-doesnt-melt-ice-heres-how-it-actually-makes-winter-streets-safe-110870" target="_blank">salt doesn't melt ice</a>.</p><p>Water freezes at 32 degrees Fahrenheit, but mixing it with salt lowers its freezing point. "The salt impedes the ability of the water molecules to form solid ice crystals," explains <a href="https://chemistry.richmond.edu/faculty/jpollock/" target="_blank">Julie Pollock</a>, assistant professor of chemistry at the University of Richmond. "The degree of freezing point depression depends on how salty the solution is." When dry salt is spread on ice, it relies on the sun or the friction of car tires to melt the ice, then keeps it from re-freezing.</p><p>Pulses of salt can harm plants, water bodies and aquatic organisms when it washes off of roads — especially during spring runoff, which can carry huge doses. Researchers are working to find more benign options, and are currently studying additives including molasses and beet juice.</p>
3. Why Trees Need Snow<p>Snow may seem like nothing but trouble, especially if you have to shovel it. But it's also a valuable resource. In the Northeast, environmental scientists <a href="https://scholar.google.com/citations?user=gS_YYI8AAAAJ&hl=en" target="_blank">Andrew Reinmann</a> and <a href="https://scholar.google.com/citations?user=LQRn9ccAAAAJ&hl=en" target="_blank">Pamela Templer</a> have found that winter snow cover <a href="https://theconversation.com/climate-change-is-shrinking-winter-snowpack-which-harms-northeast-forests-year-round-103410" target="_blank">acts like a blanket</a>, protecting tree roots and soil organisms from the cold.</p><p>In experimental forest plots where Reinmann and Templer removed snow from the ground, they have observed that</p><blockquote>"…frost penetrates a foot or more down into the soil, while it rarely extends more than two inches deep in nearby reference plots with unaltered snowpack. And just as freeze-thaw cycles create potholes in city streets, soil freezing abrades and kills tree roots and damages those that survive."<br></blockquote><p>Climate change is shortening northeast winters and decreasing snowfall, with serious effects on forests. "Losing snowpack can reduce forest growth, carbon sequestration and nutrient retention, which will have important implications for climate change and air and water quality all year-round," Reinmann and Templer predict.</p><span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="f2103debd516dacfa28999766a123d16"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/sPd4PaY9Ds4?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
4. Frozen Reservoirs<p>Snow is even more valuable in western states, where many communities get large shares of their drinking water from snowpack that lingers at high altitudes well into the warm months. Here, too, warming winters mean less snow, and scientists are <a href="https://theconversation.com/climate-change-will-mean-more-multiyear-snow-droughts-in-the-west-121406" target="_blank">already observing "snow droughts</a>."</p><p><a href="https://scholar.google.com/citations?user=NpvW4oYAAAAJ&hl=en" target="_blank">Adrienne Marshall</a> a research fellow studying hydrology and climate change at the University of Idaho, defines a snow drought as a year with snowpack so low that historically it would only happen once every four years or less.</p><p>"Today, back-to-back snow droughts in the western U.S. occur around 7% of the time," she writes. "By mid-century, if greenhouse gas emissions continue to increase, our results predict that multiyear snow droughts will occur in 42% of years on average."</p><p>Snowpack is also melting earlier in the spring, which means less water is available in summer. These changes are affecting cities, farms, <a href="https://www.ecowatch.com/tag/forests" rel="noopener noreferrer">forests</a>, wildlife and the outdoor recreation industry across the West year-round.</p><div id="37ac0" class="rm-shortcode" data-rm-shortcode-id="A6KVZL1577291178"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1136452989642727424" data-partner="rebelmouse"><div style="margin:1em 0">Today’s #snowpack on Montgomery Pk in northern White Mtns CA, seen from down in Benton Valley. Very good snow for J… https://t.co/PrFvN50V7G</div> — Laura Cunningham (@Laura Cunningham)<a href="https://twitter.com/PaleoLaura/statuses/1136452989642727424">1559786481.0</a></blockquote></div>
5. Can We Make It Snow?<p>If nature doesn't deliver as much snow as we need, what about helping it along? Many western states and agencies have tried to do just that for years by <a href="https://theconversation.com/does-cloud-seeding-work-scientists-watch-ice-crystals-grow-inside-clouds-to-find-out-90903" target="_blank">cloud-seeding</a> — adding particles to the atmosphere that are thought to serve as artificial ice crystals, promoting the formation of snow.</p><p>There's just one hitch: No one has proved it actually works. Nonetheless, "Western states need water, and many decision-makers believe that cloud seeding can be a cost-effective way to produce it," write atmospheric scientists <a href="https://scholar.google.com/citations?user=rHjhWTUAAAAJ&hl=en" target="_blank">Jeffrey French</a> and <a href="https://scholar.google.com/citations?user=T1CgJmQAAAAJ&hl=en" target="_blank">Sarah Tessendorf</a>.</p><p>In a 2018 study, French, Tessendorf and colleagues used new computer modeling tools and advanced radar to see whether they could detect ice crystals forming on silver iodide particles injected into clouds. They hung imaging probes from the wings of research planes, which flew in and out of the seeded areas of clouds. Sure enough, in those zones ice crystal formation increased by hundreds, leading to the formation of snow. No such results occurred in non-seeded regions.</p><p>More research is needed to see whether cloud seeding can change water balances over large areas. And ultimately, even if that proves to be true, another question will remain: Whether it's worth the cost.</p>
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By Jeremy Deaton
Early this week, record cold blasted the Northeast, as Boston, Massachusetts saw a high of 10 degrees F, and nearby Worcester saw the temperature top out at just 1 degree F. Meteorologists say this is just the beginning of a lengthy stretch of freezing weather.