11 Vitamin D Myths and Facts
How much do you really know about the sunshine vitamin?
Borrowed from Everyday Health by – Leslie Barrie
Medically Reviewed by Justin Laube, MD
Last Updated: December 8, 2020
Sunshine is the best natural source of vitamin D.Getty Images
With the possible exception of C, there’s perhaps no vitamin more frequently discussed than the sunshine one — aka vitamin D.
It’s no wonder: Vitamin D is a workhorse nutrient. According to the National Institutes of Health (NIH), among its functions are strengthening bones, absorbing calcium, and bolstering immunity.
Still, with all that chatter come some misconceptions. “There’s an expectation that vitamin D is a miracle drug, and that if we all just take megadose of it, it will solve all problems,” says Anne McTiernan, MD, PhD, a professor of epidemiology at the Fred Hutchinson Cancer Research Center in Seattle and the author of Starved: A Nutrition Doctor’s Journey From Empty to Full. That, of course, simply isn’t true. There’s no vitamin or supplement that is a cure-all, health experts agree.
1. Myth: The More Vitamin D You Get, the Better
Too much of a good thing can be a bad thing, and so it goes with vitamin D.
“While it is rare to get too much vitamin D, it’s not that it can’t happen, and this situation — a vitamin D toxicity — has serious health consequences,” says Amy Kimberlain, RDN, a spokesperson for the Academy of Nutrition and Dietetics and a certified diabetes care and education specialist (CDCES) based in Miami.
The most common way this happens is by taking too high a dosage of vitamin D supplements.
The NIH recommends that adults ages 19 to 70 take in 15 mcg (600 IU) and adults ages 71 and older take 20 mcg (or 800 IU). The maximum daily limit is 4,000 IU for people age 9 and older, Kimberlain says, but Harvard Health Publishing notes that an increasing number of people are taking more than this upper recommendation.
“Vitamin D increases calcium absorption, and therefore toxicity is marked by a buildup of calcium in the body,” says Kimberlain. Symptoms of vitamin D toxicity may include nausea, vomiting, frequent urination, weakness, bone pain, and kidney pain, according to the Mayo Clinic.
When choosing a supplement, check the IU on the bottle. Ideally, consult your doctor for a blood test to identify whether you need a supplement in the first place. MedlinePlus notes that they can check your levels with a simple blood test. And if you do need more of the sunshine vitamin, work with your provider to figure out the best supplement and IU for your individual health.
2. Fact: Getting Out in the Sun Helps Your Body Produce Vitamin D
Thomas Barwick/Getty Images
It’s called the “sunshine vitamin” for a reason. When the sun’s ultraviolet B light hits you, it turns a chemical in your skin into vitamin D3, according to Harvard Health Publishing. Vitamin D3 is transferred from your liver to your kidneys, where it becomes an active form of vitamin D that’s usable in your body.
Most people get some of their vitamin D through sun exposure, according to the NIH, but factors like the season, time of day, cloud cover, skin pigment, and sunscreen affect how much vitamin D a person can synthesize via the sun. For example, the NIH notes that people with darker skin aren’t able to produce as much vitamin D through sunlight.
“People would get sufficient vitamin D with daily sun exposure, but with large cities blocking light, an increase in indoor activities, clothing covering much of our bodies, or daily use of sunscreen, we don’t get that natural source of vitamin D,” says Dr. McTiernan. “Many of us can benefit from supplementation.”
Experts suggest that about 5 to 30 minutes of daily sun exposure, particularly between 10 a.m. and 4 p.m., or at least twice a week, on the arms, face, legs, and hands without sunscreen usually leads to a sufficient amount of vitamin D.
But avoid too much sun exposure, which increases your chances of skin cancer and wrinkles, by wearing sunscreen with at least SPF 15 along with protective clothing, notes the NIH. Because not every inch of your body will be covered, you’ll likely still allow your body to synthesize a sufficient amount of vitamin D.
3. Myth: It’s Easy to Get Enough Vitamin D Through Food Alone
Getting your vitamin D fix solely through food isn’t impossible, but it can be tricky because few foods contain ample D, Kimberlain says.
Excellent food sources of vitamin D include fish, such as 3 ounces of salmon, or ½ cup of white mushrooms exposed to UV light, according to the NIH.
But among the most common vitamin D foods eaten in the United States are eggs, cheddar cheese, fortified foods such as milk and cereal, and portobello mushrooms. These foods cover only a fraction of the daily value (DV) for vitamin D. For example, one large egg offers 1.1 mcg (44 IU), and vitamin D–fortified cereal offers 2 mcg (80 IU), providing 6 percent and 10 percent of the DV, respectively. This makes these foods only minor sources of the vitamin.
Think of noshing on vitamin D foods as just one step in your quest to get enough of the sunshine vitamin. “Fueling up with foods that naturally have vitamin D and those that are fortified vitamin D will provide some vitamin D; however, getting some of your vitamin D through sunlight and taking a supplement can help you reach sufficient levels,” says Kimberlain.
4. Fact: Having Low Vitamin D Is Linked to a Bad Mood
If you’re feeling low, you may want to get your vitamin D levels checked.
According to a study using rat brain cells published in July 2018 in Genes and Nutrition, vitamin D seems to play a role in the production of serotonin. Serotonin is a hormone that helps regulate mood and sleep per Stanford University. There are correlations between low vitamin D levels and mood disorders, research shows. What’s more, a study published in September 2017 in the Journal of Diabetes Research found that a vitamin D supplement improved the mood of women with type 2 diabetes (a group of people at a higher risk of depression than the general population, according to the Mayo Clinic), yet overall the data is mixed on whether vitamin D supplements for people with lower levels will prevent or help treat mood and psychiatric disorders.
There are many causes of depression, but Cleveland Clinic notes that depression and fatigue may be a sign you have low levels of vitamin D, and getting your vitamin D in the normal range may help. Still, there are challenges with the connection. “Sunlight improves both vitamin D and mood, so we wouldn’t know if it’s really the vitamin D improving the mood versus the sunlight improving mood,” says McTiernan.
5. Myth: Vitamin D Supplements Lead to Weight Loss
While there is a correlation between obesity and vitamin D deficiency, as the NIH notes, there’s no scientific proof that taking a vitamin D supplement will help trim your waistline, says Michael Holick, MD, PhD, an endocrinologist and the director of the Bone Health Care Clinic at Boston University Medical Center.
A previous study found that when obese and overweight women brought their vitamin D levels up to a normal level with a supplement, while eating a low-calorie diet and exercising, they lost more weight than women who were also on a low-calorie diet and exercising but were unable to raise their vitamin D up to the ideal level. Still, the researchers agree that it’s too early to draw any conclusions that taking vitamin D can help you shed pounds, because it’s still unclear whether a low vitamin D status is a consequence of obesity or in some way involved in its cause.
Having sufficient vitamin D, though, may help people live healthier lives, which could in turn help a person lose weight. “If bone aches and pains from a vitamin D deficiency keep you from exercising, and if vitamin D supplementation allows you to exercise more because you don’t have those aches, that could help you be more active,” says Dr. Holick.
6. Fact: Vitamin D Helps Support Your Immune System
To keep your immune system functioning at its best, you’ll want to make sure you’re getting enough vitamin D.
That’s because, according to Harvard T.H. Chan School of Public Health, vitamin D may help mitigate the harmful inflammatory response of certain white blood cells, as well as increase the immune cells’ production of microbe-fighting proteins. Adults who have low vitamin D levels are more likely to report having experienced a recent cold, cough, or upper respiratory tract infection.
“Clinical trials have found that vitamin D supplementation can reduce the amount of illnesses that children develop,” says McTiernan, referring to past research on influenza. And a meta-analysis published in February 2017 in the BMJ yielded two points: One, people who took vitamin D supplements were 12 percent less likely to develop acute respiratory infections compared with people who didn’t. And two, the authors found that for those with a severe vitamin D deficiency, taking vitamin D supplements lowered their respiratory infection risk by 70 percent.
Because of the potential benefits to the immune system, some people have been quick to assume vitamin D could work as a potential COVID-19 prevention tool or therapy, but it’s still too early to say. According to Harvard, there is no good evidence on the topic because it is such a new virus. Still, they suggest it’s wise to keep your levels out of the low range.
One study, published in October 2020 in the Journal of Clinical Endocrinology & Metabolism, found that more than 80 percent of people with COVID-19 in a hospital in Spain had a vitamin D deficiency. Another study, published in September 2020 in PLoS One, analyzed 235 individuals infected with the SARS-CoV-2 virus; the researchers concluded that improving vitamin D status in both the general population as well as those hospitalized with COVID-19 had the potential to reduce the severity of symptoms and death associated with the disease. Given the low risk of supplementation, if you have questions about taking vitamin D and proper dosing, it’s best to discuss with your primary care provider or a registered dietitian who is well versed in integrative medicine.
7. Myth: Everyone Should Get Their Vitamin D Levels Tested
For maintaining good health, it’s important to have your vitamin D levels in the adequate range. According to the NIH, adults need between 20 and 30 nanograms per milliliter (ng/mL) of vitamin D in their blood. While there’s no way to know if your levels are in that range without a test, that doesn’t make it necessary to get one, unless, as the Cleveland Clinic notes, you have a condition such as osteoporosis.
“Testing is becoming more common, but there is no need for widespread screening,” says Holick. “If you take the recommended amounts of vitamin D, your levels will be sufficient.”
It’s probably a good idea to talk to your doctor before you start supplementing. “I support seeing your doctor or other provider for a check of vitamin D level, and then taking a supplement if the test shows you’re lacking,” says McTiernan.
Also, according to MedlinePlus, your doctor may order a vitamin D blood test if you have low-vitamin-D symptoms, which could include bone weakness, bone softness, and fractures. Other risk factors that may signal to your doctor that you need a vitamin D test include obesity, previous gastric bypass surgery, older age, a dark complexion, and lack of sunlight in your day (for example, if you’re on bedrest or have an injury that keeps you indoors), MedlinePlus notes.
8. Fact: Getting Enough Vitamin D May Improve Blood Sugar Levels
If you’re trying to prevent or manage type 2 diabetes, it might be time to ask your doctor about your vitamin D levels.
“We think vitamin D helps with insulin resistance,” says Holick. For example, one review of literature published in September 2019 in the journal Current Diabetes Reports showed that low vitamin D blood levels correlated with insulin resistance. At the same time, the study authors concluded that the role of vitamin D for preventing and treating diabetes remains to be seen.
Another study published in September 2019, in the European Journal of Endocrinology, found that six months of vitamin D supplementation did improve insulin sensitivity in people at risk for developing type 2 diabetes as well as people who had been recently diagnosed. The researchers even suggested that supplementing with vitamin D may help delay the development of type 2 diabetes or slow the progression of the disease.
Given the mixed results, ask your healthcare team about possibly adding a vitamin D supplement to your diet for preventing or treating diabetes.
9. Fact: Adequate Vitamin D Is Linked With a Lower Risk of Certain Cancers
“Individuals with very low vitamin D levels are thought to be at increased risk for breast, colon, kidney, lung, and pancreatic cancers,” says Carol Fabian, MD, an oncologist at the University of Kansas Cancer Medical Center in Kansas City and the chair of its cancer prevention research program. The Cleveland Clinic notes, too, that vitamin D may help lower the risk for prostate cancer.
The most at-risk groups are individuals who are obese or have darker pigmented skin and have lower levels of vitamin D but are not supplementing, notes Dr. Fabian. Other factors can also drive up the risk. “Most people who are obese do not exercise much, and obesity and a sedentary lifestyle are also risk factors for breast, colon, kidney, lung, and pancreatic cancers,” says Fabian. While vitamin D deficiency may not be directly upping cancer risk, an association between the two exists in some cases.
That said, a review published in May 2020 in Seminars in Cancer Biology suggests that there is strong data supporting a protective effect of vitamin D (due to its role in regulating cells) against several types of cancer.
Furthermore, research shows the potential positive effects of maintaining adequate levels of vitamin D. Overall, individuals with the highest levels (greater than or equal to 35 ng/mL of vitamin D) may have about a 30 percent lower risk of breast cancer compared with those with the lowest blood levels of vitamin D (less than 15 ng/ml), says Fabian. And missing out on important UVB rays during the crucial sunny months may also up your odds of cancer. “A very large observational study with many years of follow-up suggests that women who have very low levels of vitamin D measured in the spring and summer are at increased risk for breast cancer,” says Fabian, referring to the Nurses’ Health Study, published in September 2016 in Cancer Research.
Right now, there are challenges to vitamin D and cancer studies, a review published in October 2018 in Trends in Cancer Research noted. For example, the amounts of vitamin D provided to study participants varies greatly from study to study, and men and women respond to vitamin D supplementation in different ways.
As for utilizing vitamin D to treat cancer? The research and technology isn’t there yet. “High doses of drugs with a structure similar to vitamin D may someday be used to treat some forms of breast cancer, but doses of vitamin D that are high enough to cause death of cancer cells are likely to cause very high blood levels of calcium, which can be toxic to the body,” says Fabian.
10. Myth: All Adult Women Need the Same Amount of Vitamin D
In actuality, certain women may need more or less of the sunshine vitamin. Pregnant women in particular may benefit from a supplement.
A study published in October 2016 in the Journal of Clinical Endocrinology and Metabolism found that women who give birth in the winter and have a vitamin D deficiency in early pregnancy, or gain more weight than normal during pregnancy, may need higher doses of vitamin D than other pregnant women. If any of those characteristics apply to you, ask your doctor whether you need to increase vitamin D intake.
Furthermore, the American College of Obstetricians and Gynecologists notes that severe maternal vitamin D deficiency during pregnancy is linked with congenital rickets and fractures, among other conditions, in the newborn, although this is rare. Also, the organization states that most experts agree 1,000 to 2,000 IU per day of vitamin D is safe for pregnant women.
There’s other evidence, too, that vitamin D is important for the health of the mother and baby. A review published in June 2020 in Clinical Nutrition found that vitamin D supplementation may be useful in preventing preeclampsia.
11. Fact: Age Affects Your Skin’s Ability to Make Vitamin D
Speaking of some women needing different amounts of vitamin D, older women (and men) will likely require more vitamin D. As mentioned, the recommended amount, according to the NIH, is 800 IU per day for men and women over 70.
The reason they need more: According to Johns Hopkins, older people don’t absorb vitamin D as well, and create less of it, than younger individuals. A review of research published in Endocrinology and Metabolism Clinics of North America noted that aging reduces vitamin D production in skin, and treatment of elderly people with 800 IU of vitamin D per day can increase levels to an adequate range and reduce fractures.
Still, scientists don’t suggest that the elderly megadose. Not only is it important to talk to your doctor before starting any supplement, but a study published in January 2019 in the American Journal of Clinical Nutrition showed that large doses of vitamin D (above recommended levels) were not any more effective at increasing bone mineral density than smaller doses.
No matter what you do, despite its overall low risk, it’s best to talk with your doctor or informed healthcare practitioner before you start taking a vitamin D supplement — not only might he or she have further recommendations about how much vitamin D is right for you, but you also may be able to get brand recommendations. Because the U.S. Food and Drug Administration doesn’t regulate supplements as rigorously as traditional medications, getting a brand recommendation from your doctor can be helpful.