By Franziska Spritzler
Vitamin D is extremely important for good health.
As a hormone, it plays several roles in keeping your body's cells healthy and functioning the way they should.
Most people don't get enough vitamin D, so supplements are common.
However, it's also possible—although rare—for this vitamin to build up and reach toxic levels in the body.
This article discusses six potential side effects of getting excessive amounts of this important vitamin.
Deficiency and Toxicity
Vitamin D is involved in calcium absorption, immune function and protecting bone, muscle and heart health. It occurs naturally in food and can also be produced by your body when your skin is exposed to sunlight.
Yet aside from fatty fish, there are few foods rich in vitamin D. What's more, most people don't get enough sun exposure to produce adequate vitamin D.
Supplements are very common and both vitamin D2 and vitamin D3 can be taken in supplement form. Vitamin D3 is produced in response to sun exposure and is found in animal products, whereas vitamin D2 occurs in plants.
Vitamin D3 has been found to increase blood levels significantly more than D2. Studies have shown that each additional 100 IU of vitamin D3 you consume per day will raise your blood vitamin D levels by 1 ng/ml (2.5 nmol/l), on average (2, 3).
However, taking extremely high doses of vitamin D3 for long periods of time may lead to excessive buildup in the body.
Vitamin D intoxication occurs when blood levels rise above 150 ng/ml (375 nmol/l). Because the vitamin is stored in body fat and released into the bloodstream slowly, the effects of toxicity may last for several months after you stop taking supplements (4).
Importantly, toxicity isn't common and occurs almost exclusively in people who take long-term, high-dose supplements without monitoring blood levels.
It's also possible to accidentally consume too much vitamin D by taking supplements that contain much higher amounts than are listed on the label.
In contrast, you cannot reach dangerously high blood levels through diet and sun exposure alone.
Below are the six main side effects of too much vitamin D.
1. Elevated Blood Levels
Achieving adequate levels of vitamin D in your blood may help boost immunity and protect you from diseases like osteoporosis and cancer (5).
However, there isn't universal agreement on the optimal range for these levels.
Although a vitamin D level of 30 ng/ml (75 nmol/l) is typically considered adequate, the Vitamin D Council recommends maintaining levels of 40–80 ng/ml (100–200 nmol/l) and states that anything over 100 ng/ml (250 nmol/l) may be harmful (6, 7).
Despite the fact that more people are now taking vitamin D supplements, it's rare to find someone with very high blood levels of this vitamin.
One recent study looked at data from more than 20,000 people over a 10-year period. It found that only 37 people had levels above 100 ng/ml (250 nmol/l). Only one person had true toxicity, at 364 ng/ml (899 nmol/l) (8).
In one case study, a woman had a level of 476 ng/ml (1,171 nmol/l) after taking a supplement that gave her 186,900 IU of vitamin D3 per day for two months (9).
This was a whopping 47 times the generally recommended safe upper limit of 4,000 IU per day.
The woman was admitted to the hospital after she experienced fatigue, forgetfulness, nausea, vomiting, slurred speech and other symptoms (9).
Although only extremely large doses can cause toxicity so rapidly, even strong supporters of these supplements recommend an upper limit of 10,000 IU per day (3).
Summary: Vitamin D levels greater than 100 ng/ml (250 nmol/l) are considered potentially harmful. Toxicity symptoms have been reported at extremely high blood levels resulting from megadoses.
2. Elevated Blood Calcium Levels
Vitamin D helps your body absorb calcium from the food you eat. In fact, this is one of its most important roles.
However, if vitamin D intake is excessive, blood calcium may reach levels that cause symptoms that are not only unpleasant, but dangerous.
Symptoms of hypercalcemia or high blood calcium levels, include:
- Digestive distress, such as vomiting, nausea and stomach pain
- Fatigue, dizziness and confusion
- Excessive thirst
- Frequent urination
The normal range of blood calcium is 8.5–10.2 mg/dl (2.1–2.5 mmol/l).
In one case study, an older man with dementia who received 50,000 IU of vitamin D daily for six months was repeatedly hospitalized with symptoms related to high calcium levels (10).
In another, two men took improperly labeled vitamin D supplements, leading to blood calcium levels of 13.2–15 mg/dl (3.3–3.7 mmol/l). What's more, it took a year for their levels to normalize after they stopped taking the supplements (11).
Summary: Taking too much vitamin D may result in excessive absorption of calcium, which can cause several potentially dangerous symptoms.
3. Nausea, Vomiting and Poor Appetite
Many side effects of too much vitamin D are related to excessive calcium in the blood.
These include nausea, vomiting and poor appetite.
However, these symptoms don't occur in everyone with elevated calcium levels.
One study followed 10 people who had developed excessive calcium levels after they had taken high-dose vitamin D to correct deficiency.
Four experienced nausea and vomiting and three had a loss of appetite (12).
Similar responses to vitamin D megadoses have been reported in other studies. One woman had nausea and weight loss after taking a supplement from her naturopath that was found to contain 78 times more vitamin D than stated on the label (13, 14).
Importantly, these symptoms occurred in response to extremely high doses of vitamin D3, which led to calcium levels greater than 12 mg/dl (3.0 mmol/l).
Summary: High-dose vitamin D therapy has been found to cause nausea, vomiting and lack of appetite for some due to high blood calcium levels.
4. Stomach Pain, Constipation or Diarrhea
Stomach pain, constipation and diarrhea are common digestive complaints that are often related to food intolerances or irritable bowel syndrome.
However, they can also be a sign of elevated calcium levels caused by vitamin D intoxication (15).
These symptoms may occur in those receiving high doses of vitamin D to correct deficiency. As with other symptoms, response appears to be individualized even when vitamin D blood levels are similarly elevated.
In one case study, a boy developed stomach pain and constipation after taking improperly labeled vitamin D supplements, whereas his brother experienced elevated blood levels without any other symptoms (16).
In another case study, an 18-month-old child who was given 50,000 IU of vitamin D3 for three months experienced diarrhea, stomach pain and other symptoms. These symptoms resolved after the child stopped taking the supplements (17).
Summary: Stomach pain, constipation or diarrhea may result from large vitamin D doses that lead to elevated calcium levels in the blood.
5. Bone Loss
Because vitamin D plays an important role in calcium absorption and bone metabolism, getting enough is crucial for maintaining strong bones.
However, too much vitamin D can also be detrimental to bone health.
To protect yourself against bone loss, avoid taking excessive vitamin D supplements and take a vitamin K2 supplement. You can also consume foods rich in vitamin K2, such as grass-fed dairy and meat.
Summary: Although vitamin D is required for calcium absorption, high levels may cause bone loss by interfering with vitamin K2 activity.
6. Kidney Failure
Excessive vitamin D intake frequently results in kidney injury.
In one case study, a man was hospitalized for kidney failure, elevated blood calcium levels and other symptoms that occurred after he received vitamin D injections prescribed by his doctor (20).
In one study of 62 people who received excessively high-dose vitamin D injections, each person experienced kidney failure — whether they had healthy kidneys or existing kidney disease (21).
Kidney failure is treated with oral or intravenous hydration and medication.
Summary: Too much vitamin D may lead to kidney injury in people with healthy kidneys, as well as in those with established kidney disease.
The Bottom Line
Vitamin D is extremely important for overall health. Even if you follow a healthy diet, you may require supplements in order to achieve optimal blood levels.
However, it is also possible to have too much of a good thing.
Make sure to avoid excessive doses of vitamin D. Generally speaking, 4,000 IU or less per day is considered safe as long as your blood values are being monitored.
In addition, make sure you purchase supplements from reputable manufacturers to reduce the risk of accidental overdose due to improper labeling.
If you've been taking vitamin D supplements and are experiencing any of the symptoms listed in this article, consult a healthcare professional as soon as possible.
Reposted with permission from our media associate Authority Nutrition.
In celebration of Earth Day, a star-studded cast is giving fans a rare glimpse into the secret lives of some of the planet's most majestic animals: whales. In "Secrets of the Whales," a four-part documentary series by renowned National Geographic Photographer and Explorer Brian Skerry and Executive Producer James Cameron, viewers plunge deep into the lives and worlds of five different whale species.
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="b102b19b2719f50272ab718c44703dd0"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/xOySOlB78dM?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
Herring are a primary food source for Norway's orcas. Luis Lamar / National Geographic for Disney+
Belugas are extremely social creatures with a varied vocal range. Peter Kragh / National Geographic for Disney+
A Southern Right whales is pictured in the accompanying book, "Secrets of the Whales." Brian Skerry / National Geographic
The coronavirus has isolated many of us in our homes this year. We've been forced to slow down a little, maybe looking out our windows, becoming more in tune with the rhythms of our yards. Perhaps we've begun to notice more, like the birds hopping around in the bushes out back, wondering (maybe for the first time) what they are.
A Coeligena helianthea hummingbird is photographed during a birdwatching trail at the Monserrate hill in Bogota on November 11, 2020. Colombia is the country with the largest bird diversity in the world, home to about 1,934 different bird species, a fifth of the total known. JUAN BARRETO / AFP / Getty Images
1. Choosing the Right Binoculars<p>Binoculars are a relatively indispensable tool for most birders – but, for those just starting out, it might not yet be worth the several-hundred-dollar investment. If you aren't able to scour the attics of friends or borrow a pair from a fellow bird watcher, some local birding and naturalist groups have <a href="https://vashonaudubon.org/all-about-vashon-birds/binoculars-check-out/" target="_blank">binocular loaning programs</a> for members, allowing you to plan ahead for a day (or week) of birding.</p><p>When you're ready to take the plunge, choosing a pair or binoculars should take some careful deliberation based on your needs and preferences; some <a href="https://www.birdwatchersdigest.com/bwdsite/explore/optics/top-10-tips-buying-binoculars-bird-watching.php" target="_blank">major considerations</a> might include size, ease of use, <a href="https://www.rei.com/learn/expert-advice/binoculars.html" target="_blank" rel="noopener noreferrer">magnification</a>, and price. While professional binoculars can easily run north of $1,000, there are plenty of perfectly suitable entry-level binoculars under $200. You might not get the perfect precision and clarity of more elite models, but a less expensive pair will allow you to strengthen your birding skills while deciding if you're interested in investing in a premium pair.</p><p>For a budget-friendly option, check out resale options on eBay, Facebook marketplace, or neighborhood yard sales: you might find a nicer pair whose retail price isn't within your budget.</p>
2. Know What Birds Are in Your Area<p>When I began to pay more attention to the birds just outside my apartment building, I started to learn what species have always been around me: European starlings, house sparrows, blue jays, black capped chickadees, and the occasional red-bellied woodpecker. They had always been there, but I hadn't ever taken the time to identify them. Once you learn to <a href="https://www.audubon.org/news/get-know-these-20-common-birds_" target="_blank" rel="noopener noreferrer">recognize common birds</a> in your area, you'll be able to identify the typical species right outside your window and in your community. Of course, permanent residential birds in your neighborhood will <a href="https://nestwatch.org/learn/focal-species/" target="_blank" rel="noopener noreferrer">vary by region</a>, as will those migrating through it.</p>
3. Get Out and Explore<p>Venturing elsewhere might allow you to spot some different species beyond those frequenting your backyard. Anywhere with water or greenery offers a place for birding; as an urbanite myself, I've found that even small- and mid-sized parks in New York City allow me to find more elusive birds (although Central Park takes the crown for an afternoon of urban birding).</p><p>If you are able to travel a bit further from home, <a href="https://www.fws.gov/refuges/" target="_blank">national wildlife refuges</a> and <a href="https://www.americasstateparks.org/" target="_blank" rel="noopener noreferrer">state/national parks</a> are excellent places to explore bird habitats and perhaps log some less-common sightings. The American Birding Association also lists <a href="https://www.aba.org/aba-area-birding-trails/" target="_blank" rel="noopener noreferrer">birding trails by state</a>, and Audubon and BirdLife International identify <a href="https://www.audubon.org/important-bird-areas" target="_blank" rel="noopener noreferrer">Important Bird Areas (IBAs)</a> across the country – important bird habitats and iconic places that activists are fighting to protect – where birders can spot birds of significance.</p>
4. Finding a Bird: Stop, Look, Listen, Repeat<p>The National Audubon Society recommends the "<a href="https://www.audubon.org/news/how-find-bird" target="_blank">stop, look, listen, repeat</a>" mantra when seeking and identifying birds.</p><p>First and foremost, spotting birds requires attention. Stopping – getting out of the car, pausing on the sidewalk, trail, or in the backyard to look up – is the most important step.</p><p>When looking for birds, try to avoid gazing wildly around; rather, scan your surroundings, focusing on any odd shapes or shadows, trying to think about where a bird might perch (power lines, fence posts, branches), or keep an eye on the sky for flying eagles and hawks. In open areas like fields and beaches, you might have a more panoramic view, and can take in different sections of the landscape at a time. Look around with the naked eye before reaching for the binoculars to hone in.</p><p>While it can be hard to sift through the noise, listening for birds is perhaps an even more important element of bird watching than looking. Once you spend more time in the field, you'll be able to parse apart the racket and identify specific species, especially aided by Audubon's Bird Guide app or by learning from their <a href="https://www.audubon.org/section/birding-ear" target="_blank">Birding by Ear series</a>.</p><p>Repeat this pattern as you continue on your way, stopping to look and listen for birds as you go, rather than waiting for them to come to you. </p>
5. Identification<p>When you head out for a day of bird watching – especially when you're hoping to spot some new species – you'll want to be armed with the tools to identify what you see. <a href="https://www.audubon.org/news/how-identify-birds" target="_blank" rel="noopener noreferrer">Major considerations when identifying birds</a> are their group (such as owls, hawks, or sparrow-like birds), size and shape, behavior, voice, field marks, season, and habitat.</p><p>The <a href="https://www.sibleyguides.com/about/the-sibley-guide-to-birds/" target="_blank" rel="noopener noreferrer">Sibley Guide to Birds</a> and the <a href="https://www.hmhbooks.com/shop/books/peterson-field-guide-to-birds-of-north-america-second-edition/9781328771445" target="_blank" rel="noopener noreferrer">Peterson Field Guide</a> are widely considered the best books for identifying birds in North America, although many <a href="https://www.audubon.org/news/what-bird-guide-best-you" target="_blank" rel="noopener noreferrer">specialized guides</a> focus on specific species or regions as well.</p><p>Plenty of <a href="https://blog.nature.org/science/2013/05/27/boucher-bird-blog-apps-smart-birder/" target="_blank" rel="noopener noreferrer">bird identification apps</a> have popped up in recent years – including National Geographic Birds, Sibley eGuide to Birds, iNaturalist, Merlin Bird ID, and Birdsnap – which are basically a <a href="https://www.audubon.org/news/the-best-birding-apps-and-field-guides" target="_blank" rel="noopener noreferrer">field guide in your pocket</a>. I'm partial to the Audubon Bird Guide, which allows users to filter by common identifiers, including a bird's habitat, color, activity, tail shape, and general type, adding them all to a personal map to view your sightings.</p>
6. Recording Your Sightings<p><span>As you deepen your commitment to birding, you might join the community of birders that track and quantify their sightings, building their </span><a href="https://www.thespruce.com/what-birds-count-on-a-life-list-386704#:~:text=A%20life%20list%20is%20a,which%20birds%20you%20have%20seen." target="_blank" rel="noopener noreferrer">life list</a><span>.</span></p><p>While a standard notebook noting the date, species name, habitat, vocalizations, or any other data you wish to include will suffice, some birders opt for a more <a href="https://www.riteintherain.com/no-195-birders-journal" target="_blank" rel="noopener noreferrer">structured birder's journal</a> with pre-determined fields to record your encounters, take notes, draw sketches, etc.</p><p>Many birders also choose to record their sightings online and in shared databases (which include many of the field guide apps), often pinpointing them on a map for others to view. Launched by the Cornell Lab of Ornithology and Audubon, <a href="https://ebird.org/home" target="_blank" rel="noopener noreferrer">eBird is one of the largest databases and citizen science projects around birding</a>, where hundreds of thousands of birders enter their sightings, and users can explore birds in regions and hotspots around the world. Users can also record their sightings on the <a href="https://apps.apple.com/us/app/ebird/id988799279" target="_blank" rel="noopener noreferrer">eBird app</a>.</p>
7. Attracting Birds to Your Own Yard<p>Feeding birds is a common phenomenon: more than 40% of Americans maintain a birdfeeder to attract birds and watch them feast.</p><p>Not all birdfeed is created equal, however. Many commercial varieties are mostly made with "fillers" (oats, red millet, etc.) that birds will largely leave untouched. After researching what birds to expect in your area – and which ones you want to attract – you can create your own birdfeed with <a href="https://www.allaboutbirds.org/news/types-of-bird-seed-a-quick-guide/?pid=1142" target="_blank">seeds that will appeal to them</a>.</p><p>Beyond filling a birdfeeder, <a href="https://www.ecowatch.com/eco-friendly-lawn-2651194858.html" target="_self">transforming your yard into an eco-friendly oasis</a> is by far the best way to attract birds. Choosing to forgo mowing your lawn, planting native flowers and grasses, and ditching the pesticides will bring back the bugs that birds feed on, and provide a safe haven in which birds can happily live and eat.</p><p>While it's widely considered acceptable – and even beneficial – to feed birds with appropriate seeds, communal birdfeeders often <a href="https://www.audubon.org/news/to-feed-or-not-feed" target="_blank" rel="noopener noreferrer">foster unlikely interactions between different species</a>, who can then transmit harmful diseases and parasites to one another. Maintaining several bird feeders with different types of seeds might keep different species from coming into contact, and feeders can be <a href="https://www.allaboutbirds.org/news/how-to-clean-your-bird-feeder/" target="_blank" rel="noopener noreferrer">cleaned to prevent the spread of infection</a>.</p>
8. Inclusivity and Anti-Racism in the Birding Community<p>Like all outdoor activities and areas of scientific study, birding communities are subject to racist and discriminatory ideologies. Black birders have long experienced discrimination and underrepresentation in outdoor spaces. The work of organizations like the <a href="https://www.instagram.com/birdersfund/" target="_blank">Black & Latinx Birders Fund</a>, <a href="https://www.instagram.com/birdability/" target="_blank">Birdability</a>, and <a href="https://www.instagram.com/feministbirdclub/" target="_blank">Feminist Bird Club</a> highlight the contributions and importance of birders of color, birders with disabilities, and women and LGBTQ+ birders to the birding community, as do activists and naturalists like <a href="https://www.instagram.com/hood__naturalist/" target="_blank">Corina Newsome</a> and <a href="https://www.instagram.com/tykeejames/" target="_blank">Tykee James</a>. The work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a>, <a href="https://camilledungy.com/publications/" target="_blank">Camille Dungy</a> (read her poem <a href="https://www.poetryfoundation.org/poetrymagazine/poems/58363/frequently-asked-questions-10" target="_blank">Frequently Asked Questions: 10</a>), and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank">Birding While Black</a>" – are a great place to start.</p><p>Getting involved in birding means educating ourselves on these issues and taking meaningful action; the work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a> and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank" rel="noopener noreferrer">Birding While Black</a>" – are a great place to start. Just as birders are activists for protecting habitats and natural areas, we must also be active and aware of inclusivity in these spaces.</p>
9. Get Involved<p>To learn from and enjoy the company of other birders, check out local birding groups in your area to join. Many Audubon chapters host trips, meetings, and bird walks for members. The American Birding Association even maintains a <a href="https://www.aba.org/festivals-events/" target="_blank">directory of birding festivals</a> across the country.</p><p>Volunteering for birds is also a great way to meet other birders and take action for birds in your community; local organizations might have opportunities for assisting with habitat restoration or helping at birding centers.</p><p>Like all wildlife, climate change and habitat destruction threaten the livelihood of birds, eliminating their breeding grounds and food sources. A <a href="https://www.audubon.org/climate/survivalbydegrees" target="_blank">2019 report released by the National Audubon Society</a> found that two-thirds of North American birds may face extinction if global temperatures rise 5.4 degrees Fahrenheit by 2100. Staying informed about and taking action for legislation designed to protect birds and our climate – such as the recent <a href="https://www.congress.gov/bill/116th-congress/house-bill/5552/text" target="_blank" rel="noopener noreferrer">Migratory Bird Protection Act</a> – is important for ensuring a livable future for wildlife and humans alike.</p><p><em>Linnea graduated from Skidmore College in 2019 with a Bachelor's degree in English and Environmental Studies, and now lives in Brooklyn, New York. Most recently, Linnea worked at Hunger Free America, and has interned with WHYY in Philadelphia, Saratoga Living Magazine, and the Sierra Club in Washington, DC. </em><em>Linnea enjoys hiking and spending time outdoors, reading, practicing her German, and volunteering on farms and gardens and for environmental justice efforts in her community. Along with journalism, she is also an essayist and writer of creative nonfiction.</em></p>
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