26 Side Effects of Low Vitamin D You Need to Know About

From depression to cancer, many conditions go along with vitamin D deficiency.

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No doubt you've seen the headlines promoting the negative side effects of low vitamin D levels. It's important to read those stories carefully, since links don't necessarily prove cause and effect. "There can be many other explanations for the associations observed," says JoAnn Manson, MD, PhD, chief of the division of preventive medicine at Brigham and Women's Hospital in Massachusetts.

That said, not getting enough vitamin D can lead to negative health consequences. The good news? It's relatively easy to get enough vitamin D. Certain foods, including fatty fish, can help you increase your levels, as can sunlight. Specifically, 15 minutes of sunlight on your hands and face each day can do the trick, Donald Ford, MD, a family medicine doctor at Cleveland Clinic, previously told Health. (Also worth noting, if it's raining one day, you can make up for it by spending 30 minutes in the sun the next.)

Here are 27 reasons you should consider spending more time outdoors if your doctor mentions that your vitamin D levels are low.

01 of 26

Obesity

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Obese men, women, and children are 35% more likely to be vitamin D deficient than normal-weight people, and 24% more likely to be D deficient than overweight people, according to a 2015 meta-analysis. One possible explanation: A study published in 2000 in the American Journal of Clinical Nutrition found that obesity limits the body's ability to use vitamin D from both sunlight and dietary sources, since fat cells hold on to vitamins and don't release them efficiently. Translation: Obesity could actually make vitamin D deficiency worse.

02 of 26

Diabetes

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People with diabetes or prediabetes have lower vitamin D levels than those with normal blood sugar levels, according to a Spanish study published in 2015 in the Journal of Clinical Endocrinology & Metabolism. The link held for folks across the BMI spectrum—in fact, both lean and severely obese people with diabetes or prediabetes had significantly lower D than their nondiabetic counterparts. The study's authors believe that vitamin D deficiency and obesity "interact synergistically" to increase the risk of diabetes and other metabolic disorders.

03 of 26

Heart disease

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Heart disease and vitamin D deficiency are known to go hand in hand; one sobering 2009 study published in the Journal of Clinical Endocrinology and Metabolism found that subjects with extremely low levels of vitamin D were nearly three times as likely to die of heart failure and five times as likely to die of sudden cardiac death. However, experts say there isn't evidence of a direct link between higher vitamin D levels and lowering cardiovascular risk, so it's too soon to say if taking supplements might boost heart health.

04 of 26

Lupus

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Lupus, a chronic inflammatory disease in which the body's immune system attacks its own organs and tissues, is frequently associated with vitamin D deficiency—in part because lupus patients are often advised to stay out of the sun (the source of 90% of our vitamin D), and may be prescribed corticosteroids, which are also linked to low levels of D. A recent research review suggested that correcting lupus patients' vitamin deficiencies might help to lessen the severity of their disease.

05 of 26

Preterm birth

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In a study of more than 2,000 mothers-to-be, women with higher levels of 25-hydroxy vitamin D (an indicator of our bodies' vitamin D stores, measurable with a blood test) had a lower risk of giving birth before 37 weeks. The authors suggested that D could be having a protective effect by reducing bacterial infection in the placenta, which can cause preterm birth. In another study, researchers who examined data from the Collaborative Perinatal Project (a study of more than 42,000 women) reported that among nonwhite mothers, higher concentrations of 25-hydroxy D were associated with a reduced risk of birth before 35 weeks.

06 of 26

Multiple sclerosis

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In 2013, an international team of researchers examined data from 465 people with early-stage MS, an often-disabling autoimmune disease that affects the central nervous system; they reported that higher levels of 25-hydroxy D measured at the onset of symptoms (and then 6, 12, and 24 months later) predicted a slower rate of disease progression. Subjects with higher levels of D had a slower increase in brain lesion volume, fewer new lesions, lower brain volume loss, and lower disability levels than those with low levels of D.

07 of 26

PMS

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According to the Nurses' Health Study II, women between the ages of 27 and 44 with a high intake of vitamin D had the lowest risk of experiencing PMS symptoms. (The study found that higher calcium intake was also associated with lower PMS risk.) A 2010 pilot study suggested a connection between vitamin D levels and PMS for younger women as well. Non-steroidal anti-inflammatory drugs like ibuprofen and naproxen are still the first line of therapy for PMS symptoms, but researchers believe vitamin D supplements are a promising alternative.

08 of 26

Inflammatory bowel disease

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Vitamin and mineral deficiencies, including D deficiency, are extremely common for people with gastrointestinal health issues that affect their body's ability to absorb nutrients. Patients with active ulcerative colitis, a type of inflammatory bowel disease (IBD), especially those who take corticosteroids, are often deficient in D, a study in Digestive Diseases and Sciences suggested, and some researchers believe deficiency could have a role not only in increasing the risk of developing IBD but in determining the severity of a person's symptoms.

09 of 26

Alopecia and hair loss

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Women with female pattern hair loss had significantly lower levels of vitamin D than those without hair loss, a study in Skin Pharmacology and Physiology found. The vitamin is crucial for hair cycling, and helps push hair from its resting phase to the growing phase. Turkish researchers found that patients with alopecia areata, an autoimmune disease that attacks follicles and can cause hair loss all over the body, had significantly lower levels of 25-hydroxy vitamin D than folks without the condition, and the lower their D levels, the more severe their disease.

10 of 26

Insulin resistance

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Insulin resistance, which leads to glucose buildup in the blood and type 2 diabetes and prediabetes, has been linked to vitamin D deficiency for quite some time; that said, researchers have yet to find that correcting that deficiency can correct the problem. A small study of Norwegian men and women found that vitamin D supplementation doesn't improve insulin sensitivity in healthy people, and researchers in Iran found that vitamin D supplements had no effect on insulin sensitivity in pre-diabetic patients.

11 of 26

Eczema

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Research suggests that children with atopic dermatitis, a type of eczema, have more severe symptoms the lower their vitamin D levels. Indeed, eczema tends to worsen in the winter when the air is dry and we get less sunlight (a major source of D). Supplementing with vitamin D in pill form can improve eczema—or if you're looking for an excuse to vacation, one study found that Norwegian kids with eczema who were taken to a sun-drenched subtropical island for 4 weeks experienced relief from their symptoms that lasted for 3 months after they got back home.

12 of 26

Tooth decay in infants and toddlers

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Vitamin D is crucial both to our dental health and the formation of our teeth in the first place—yet another reason taking prenatal vitamins is so important. A study in Pediatrics measured the blood levels of vitamin D in pregnant women, then checked the teeth of their babies at 1 year old. Researchers found that mothers of children with weak enamel and tooth decay had significantly lower vitamin D levels during pregnancy compared to moms of children with healthy teeth.

13 of 26

Gum disease and tooth loss

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The sunshine vitamin has a key role in protecting our teeth as we age, too; in one study, older adults who took 700 international units (IU) of vitamin D (along with calcium) each day for three years were less likely to lose teeth than those who took placebo pills, even two years after they stopped taking the supplements. Researchers have also reported strong evidence that D deficiency is a risk for gum diseaseand that it can worsen dental problems once we have them.

14 of 26

Alzheimer's and dementia

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Studies have linked low vitamin D to abnormalities in brain structure, cognitive decline, and dementia. In a recent study in JAMA Neurology, which measured vitamin D and cognitive function each year in an ethnically diverse group of elderly patients (about half of whom had some form of cognitive impairment at the start of the study), lower levels of D were associated with accelerated cognitive decline. Research is now underway to determine whether or not supplements can offer hope for prevention and treatment.

15 of 26

UTIs

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Vitamin D helps prevent infection by helping our bodies produce natural antibiotics, and a study in Archives of Disease in Childhood found that D deficiency is a risk factor for urinary tract infections in children, especially girls. It's a bit too soon to call vitamin D the new cranberry juice, but low levels are associated with UTIs for adults, too; a study of women who suffered from recurrent UTIs found that they had lower levels of vitamin D than women who didn't.

16 of 26

Female incontinence

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Since vitamin D is critical for muscle strength, deficiency can contribute to weakness in the pelvic floor—that is, the hammock of muscles that supports the bladder, vagina, uterus, and rectum—and lead to urinary incontinence (as well as, potentially, fecal incontinence) in women, according to a 2012 research review published in International Urogynecology Journal. For women who suffer from poor bladder control, maintaining healthy levels of vitamin D could prove to be as important as performing pelvic floor exercises.

17 of 26

Asthma

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According to a large Israeli study published in Allergy that tracked more than 21,000 adults with asthma, while people with asthma were no more likely to have low D than those in the general population, asthmatics who did have a vitamin D deficiency were 25% more likely to experience acute attacks and to need to see a doctor more frequently for their asthma. The study's authors say that their findings support the importance of vitamin D level screenings for patients with severe asthma—and that supplements could be necessary for those falling short.

18 of 26

Schizophrenia

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There's a strong link between vitamin D deficiency and this mental health disorder: In a 2014 review of 19 studies, researchers found that 65% of schizophrenia patients had low levels of vitamin D, and people with vitamin D deficiency were more than twice as likely to have schizophrenia. That correlation doesn't necessarily mean that deficiency causes schizophrenia. In fact, experts hypothesize that the reverse may be true, with schizophrenia causing people to make lifestyle and diet choices that lead to deficiency.

19 of 26

Depression

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Female college students who had low levels of vitamin D were more likely to have clinically significant symptoms of depression, according to a 2015 study published in Psychiatry Research. A larger meta-analysis of more than 31,000 research subjects, published in the British Journal of Psychiatry, found a correlation as well. There's hope that vitamin D supplements might help: A very small study presented to the Endocrine Society in 2012 found three women with moderate to severe depression experienced improvement in their symptoms after they received treatment for vitamin D deficiency. Experts have yet to prove vitamin D's effect on mood in large-scale clinical research—but if it can be confirmed, correcting that deficiency could make a whole lot of people a whole lot happier.

20 of 26

Colorectal cancer

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Researchers have known about a connection between vitamin D and cancer risk since the 1940s, when a researcher from the Medical College of Virginia demonstrated a link between latitude (which predicts our exposure to sunlight, our main source of D) and death from cancer. More recently, a 2011 meta-analysis that included more than 1 million study subjects found that greater vitamin D intake and higher vitamin D levels were linked to lower risk of colorectal cancer. On the other hand, a 2006 clinical trial as part of the Women's Health Initiative found that women who took calcium and vitamin D supplements for an average of seven years had no reduction in colorectal cancer risk compared to those who took a placebo. More research is needed to shed light on these mixed results.

21 of 26

Breast cancer

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Some recent evidence has suggested a link between higher levels of vitamin D and a lowered risk of breast cancer: One meta-analysis, for example, found that a small increase in vitamin D levels could reduce risk for postmenopausal women by 12%. Other studies, on the other hand, have found that blood levels of vitamin D have no link with breast cancer. A randomized trial, the VITAL study, studies effects of higher doses of vitamin D on both heart disease and cancer; those results will provide better answers about if and how it can impact risk.

22 of 26

Pancreatic cancer

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People with the highest vitamin D levels were 35% less likely to develop pancreatic cancer than those with the lowest levels, according to a 20-year study of nearly 120,000 people conducted by researchers from Brigham and Women's Hospital in Massachusetts. And in exciting news for this deadly form of cancer, researchers are currently studying how a modified form of vitamin D may help "deactivate" a certain type of cell that feeds pancreatic tumor growth, making tumors more vulnerable to treatment with chemotherapy.

23 of 26

Prostate cancer

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Low levels of vitamin D were associated with more advanced, aggressive prostate tumors in biopsy patients in a 2014 study in Clinical Cancer Research; among African American men, low vitamin D was also associated with a higher risk of developing prostate cancer in the first place. A small pilot study from the Medical University of South Carolina in Charleston found that when prostate cancer patients received 4,000 IU of vitamin D per day for 60 days, 60% of them showed improvement in their tumors.

24 of 26

Osteoporosis

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Our bodies rely on vitamin D to help absorb calcium and grow bones that stay dense and strong throughout our lives. In fact, more than 50% of women treated for bone loss have inadequate vitamin D levels. Accordingly, the National Osteoporosis Foundation recommends an intake of 400 to 800 IU of vitamin D per day for adults under the age of 50, and 800 to 1,000 IU for those over the age of 50 (the risk of osteoporosis increases with age).

25 of 26

Rickets

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Rickets, or the softening and weakening of bones in children, is usually caused by an extreme and prolonged vitamin D deficiency; children who are 3 to 36 months old are at highest risk because their bones are growing so fast. In the late 19th century, doctors realized that vitamin-D-rich cod liver oil helped to prevent and treat rickets in children; manufacturers added vitamin D to milk for the first time in the 1930s, and rickets has since become rare in the United States. When nutritional rickets is diagnosed, supplementation with calcium and vitamin D corrects most bone damage within a few months, sometimes within a few days. The American Academy of Pediatrics recommends that all infants, children, and adolescents receive a minimum daily intake of 400 IU of vitamin D.

26 of 26

Childhood language impairment

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Women who had low levels of vitamin D at 18 weeks pregnancy had nearly double the risk of having a child with signs of language impairment at ages 5 and 10 compared to women with higher levels, according to an Australian study published in Pediatrics. The results don't prove that vitamin D causes those difficulties, but they do highlight its importance in fetal brain development; it's possible that prenatal vitamin D supplementation may reduce the risk of developmental language problems in children.

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