New data suggests that the benefits of vitamin D—the sunshine vitamin—go way beyond bone health. The latest research also indicates that far more people may have a vitamin D deficiency than previously believed, as it seems the threshold for optimal vitamin D levels was historically set too low! Read on to learn vitamin D deficiency symptoms, how much vitamin D you really need, and the best sources of vitamin D.
The Discovery of Vitamin D
The discovery of vitamin D stemmed from the medical study of a childhood borne disease called rickets. You might never have heard of rickets, because it’s quite rare now, but that hasn’t always been the case.
First described in an official medical work in 1650 by Francis Glisson, rickets spiked during the Industrial Revolution when the number of children suffering from the disease climbed as high as 60% in urban areas. Then, in 1822, a researcher named Sniadecki recognized that rickets was caused by inadequate exposure to sunlight. By the mid-1800s, medical professionals had adopted cod liver oil as a highly effective treatment for rickets, and in 1919, a pair of researchers identified vitamin D as the active ingredient responsible for cod liver oil’s curative effect.
Signs and Risks of Low Vitamin D
The classic vitamin D deficiency symptoms all relate to bone health, which makes sense because your body requires adequate vitamin D saturation to absorb calcium and phosphorus, the building blocks of strong bones. When your levels drop too low, your bones can become soft, brittle, or misshapen.
It now appears that vitamin D influences far more than just the health of your bones. Ongoing investigation shows that vitamin D could play a role in immune function and insulin regulation, meaning it may help to prevent certain chronic diseases and even cancer, according to an article written by Katherine Zeratsky, a registered dietician at the Mayo Clinic.
The latest findings also establish that many people have suboptimal vitamin D levels. Data from the Centers for Disease Control and Prevention (CDC) reveal that the percentage of white American adults with optimal vitamin D levels has declined from 60% in 1988-1994 to approximately 30% in 2001-2004. Since darker skin pigmentation increases your risk of deficiency, the numbers are even more dire for African Americans. During that same time, the percentage of adults with optimal vitamin D levels fell from approximately 10% to 5%.
Here’s how some risk factors contribute to a vitamin D deficiency as well as vitamin D deficiency causes:
- Lifestyle: The less time you spend outdoors, the more likely it is that you’re not taking in enough vitamin D.
- Age: As we age, our skin becomes less efficient at producing vitamin D, making us more susceptible to deficiencies.
- Body weight: There’s a correlation between higher body fat percentages and lower vitamin D levels, so if you’re medically overweight or obese, you’re at greater risk of having low vitamin D.
- Skin tone: Natural pigments called melanin determine how light or dark your skin looks. In basic terms, more melanin means darker skin. Because melanin slows down production of vitamin D, having dark skin also increases the chances you’ll be deficient.
- Season: During the winter months, the sun is at too low an angle in the sky to generate much vitamin D production in your skin, even if you’re spending time outside. Your skin does store up vitamin D from summer sun exposure, but by late winter, deficiencies can set in, especially for people living at higher latitudes.
A 2010 article on identifying and treating vitamin D deficiency notes that while it’s “well established that many people have vitamin D levels that are less than currently recommended for optimal health,” it doesn’t make sense to universally screen for the deficiency since the tests are quite expensive. As long as patients appear to have no evidence of a true deficiency, and instead seem likely to have developed an insufficiency, the authors recommend adjusting lifestyle factors to achieve optimal levels.
Vitamin D Insufficiency vs. Vitamin D Deficiency
Even when doctors do decide to test for a vitamin D deficiency, there are serious questions about what the cutoff should be to determine a deficiency or insufficiency. In an article on vitamin D insufficiency published in Mayo Clinic Proceedings, a peer-reviewed medical journal, Dr. Tom D. Thatcher and Dr. Bart L. Clarke argue: “Reliance on a single cutoff value to define vitamin D deficiency or insufficiency is problematic because of the wide individual variability of the functional effects of vitamin D and interaction with calcium intakes.”
Thatcher and Clarke conclude that the best, most prudent approach would be for at-risk individuals to increase their vitamin D intake.
If you’re concerned about a possible deficiency or insufficiency, you may want to asses whether you show any of the following signs of low vitamin D:
- Blue mood: There’s a strong link between serotonin, the brain hormone associated with feelings of well-being and happiness, and sun exposure. A 2006 research study that enrolled 80 elderly patients found that those with the lowest levels of vitamin D were 11 times more likely to be depressed than those with more optimal levels.
- Fatigue and tiredness: Even moderately low levels of vitamin D have been shown to increase fatigue and impair quality of life, according to this large observational study. Further research supports the connection between low levels of vitamin D and tiredness.
- Bone pain and muscle weakness: Dr. Michael F. Holick, one of the preeminent experts in the field of vitamin D research, believes that many patients diagnosed with fibromyalgia may actually be vitamin D deficient. “Many of these symptoms are classic signs of vitamin D deficiency osteomalacia, which is different from the vitamin D deficiency that causes osteoporosis in adults,” Holick said. “What’s happening is that the vitamin D deficiency causes a defect in putting calcium into the collagen matrix into your skeleton. As a result, you have throbbing, aching bone pain.”
- Head sweating: This one may sound strange, but it’s one of the classic signs of vitamin D deficiency! In fact, when the deficiency was more common in childhood and associated with serious health consequences like rickets, doctors used to routinely ask new mothers whether their infant’s head was sweating.
- Frequent illnesses and infections: Vitamin D plays a crucial role in keeping your immune system functioning at peak capacity, so when your levels are low, you’re more susceptible to getting sick.
- Slow wound healing: Several studies have found a connection between vitamin D and wound healing. In 2016, a team from the Wound Healing Research Group at the University of Alberta published findings indicating that vitamin D ramps up the production of compounds needed to form new skin as part of the wound-healing process.
Lack of Vitamin D Can Lead to These 5 Illnesses
If the symptoms of vitamin D deficiency get overlooked for too long, more serious illnesses can develop. Scientists are still teasing out the connections between vitamin D and various conditions. So far, research demonstrates that vitamin D may play a role in the progression of dementia, prostate cancer, erectile dysfunction (ED), schizophrenia, and heart disease, among others. Studies also suggest a possible protective element against diabetes, high blood pressure, and multiple sclerosis, but more research needs to be conducted.
The journal Neurology published a study in 2014 linking moderate and severe vitamin D deficiency in older adults with as much as a 50% increased risk of developing Alzheimer’s disease and other forms of dementia. The study enrolled over 1,600 participants, all of whom were at least 65 years of age and none of whom had dementia at the outset. The authors found that participants with low levels of vitamin D had a 53% increased risk of developing all-cause dementia, and those with severe deficiencies had a 125% increased risk!
They also found that participants with low vitamin D levels were approximately 70% more likely to develop Alzheimer’s disease in particular.
The researchers did note that their study was observational, meaning it did not establish a causal relationship between vitamin D deficiency and dementia. Their working theory at the time was that vitamin D might clear away plaques in the brain, the growth of which gives rise to memory loss and the other symptoms of dementia.
A team of researchers from Northwestern University published findings in Clinical Cancer Research in 2014 on the relationship between low vitamin D levels and prostate cancer. After analyzing the vitamin D levels of 667 men between the ages of 40 and 79 who were undergoing prostate biopsies, the team found an especially clear link between low vitamin D and prostate cancer for African-American men.
When the disease was more progressed, they also found a connection to low vitamin D levels for white men. They believe various factors make it challenging to develop a clear rubric for using vitamin D levels as a biomarker for prostate cancer, but that it warrants further exploration. And, again, the findings were observational.
The Journal of Sexual Medicine published original research on a possible link between vitamin D levels and ED. The authors assessed the severity of participants’ conditions using the International Index of Erectile Function (IIEF-5) and classified the root causes as arteriogenic, borderline, and non-arteriogenic.
Based on a fairly small study of 143 participants, the authors found that a significant portion of the participants had low levels of vitamin D, and that those with arteriogenic ED were far more likely to have deficiencies or insufficiencies.
Arteriogenic ED is caused by insufficient arterial blood supply. The study authors hypothesized that lack of vitamin D may impede the arteries’ ability to dilate, which would be in line with the stronger association between vitamin D deficiency and arteriogenic ED.
A meta-analysis of 19 observational studies on vitamin D deficiency and schizophrenia found that individuals with a lack of vitamin D can have as much as a 50% greater risk of a schizophrenia diagnosis compared to individuals with appropriate vitamin D levels.
They found that schizophrenia is more common at high latitudes and in cold climates, which correlates with known causes of vitamin D deficiency. They noted that randomized controlled trials would be necessary to determine whether increasing vitamin D levels could help to prevent schizophrenia. Unrelated studies also support a connection between vitamin D and mental health more broadly, making this an appealing area for further research.
Two scientists from the Vascular Surgery Research Group at Imperial College in London published a literature review in an American Heart Association journal that concluded there is strong evidence to support “an independent association between vitamin D deficiency and various manifestations of degenerative cardiovascular disease.” Specifically, a lack of vitamin D appears to increase your chances of developing atherosclerosis, hypertension, diabetes, and stroke.
The authors did mention that at this time, it’s not clear whether increasing levels of vitamin D can help manage cardiovascular disease.
How Much Vitamin D Do You Need?
The way experts talk about how our bodies use vitamin D and how much vitamin D we need can be quite confusing. To properly evaluate how much vitamin D you need, it’s important to understand some basic facts about the vitamin and how your body takes it in.
There are two forms of vitamin D: vitamin D2 and vitamin D3. Vitamin D3, also called cholecalciferol, is the form your skin produces when exposed to UVB rays in sunlight. You can also get vitamin D3 from certain animal protein sources. Vitamin D2, also known as ergocalciferol, can be found in some plants. It’s also produced commercially for the irradiation of yeast and used for fortification and supplementation. Both vitamin D2 and D3 can be used for vitamin D supplementation.
Once you ingest them, your body breaks down both forms of vitamin D in the exact same way. There’s some evidence that your body breaks down vitamin D3 faster, but it appears that as long as you’re regularly getting enough, your body can use both vitamin D2 and D3 efficiently. Your liver converts both forms to 25-hydroxyvitamin D, or 25(OH)D, the compound that blood tests measure to determine vitamin D deficiency or insufficiency.
Determining a healthy vitamin D level can be challenging. Typically blood levels of 25(OH)D are measured in nanograms per milliliter, or ng/mL. In 2010, the Institute of Medicine declared that any level below 20 ng/mL was considered a vitamin deficiency that put you at risk for bone health problems. The following year, the Endocrine Society urged an even higher minimum of at least 30 ng/mL, with between 40 and 60 ng/mL identified as an optimal range.
As our understanding of the importance of vitamin D expands, and the threshold for what’s considered a deficiency continues to be adjusted, some experts propose that we treat between 50 and 70 ng/mL as the optimal range, and aim for blood levels that fall between those two points.
So, how much vitamin D do you need to take in to maintain optimal levels? Different organizations recommend different levels. Some experts believe that more evidence is needed to back recommendations for higher doses, while others believe taking lower amounts just isn’t enough. For adults, the minimum daily intake recommendations range from 600 IU (international units) to 5,000 IU and the upper limits from 4,000 IU to 10,000 IU.
The argument in favor of the higher recommendations is supported by the data on the amounts of vitamin D generated in response to sun exposure. Thatcher and Clarke state that 20 minutes of summer sun exposure on bare skin produces the equivalent of 15,000 to 20,000 IU of vitamin D3.
If you do choose to take vitamin D supplements, it’s important not to exceed maximum recommended doses. Vitamin D is fat-soluble, meaning your body does not flush it out and it can accumulate problematically. If you have a health condition that you’re seeking to treat with supplement doses over 10,000 IU daily, be sure to consult with a medical professional.
While there are foods that contain vitamin D—most notably beef liver, egg yolks, and fatty fish like tuna, mackerel, and salmon—and high-quality vitamin D supplements are available, the consensus when it comes to sources of vitamin D is that the sun truly can’t be beat.
Get Your Vitamin D from the Sun
While there are clear benefits to sunscreen use, it does prevent your skin from generating vitamin D. “People are spending less time outside and, when they do go out, they’re typically wearing sunscreen, which essentially nullifies the body’s ability to produce vitamin D,” said Dr. Kim Pfotenhauer, a researcher on a clinical review published in the Journal of the American Osteopathic Association.
The review found that nearly 1 billion people worldwide may have insufficient levels of vitamin D, and that the cause, for a large percentage of those individuals, has to do with sunscreen use. “While we want people to protect themselves against skin cancer, there are healthy, moderate levels of unprotected sun exposure that can be very helpful in boosting vitamin D,” Pfotenhauer said.
The amount of time you need in the sun to maintain optimal levels of vitamin D depends on a variety of factors, including age, weight, skin color, diet, antioxidant levels, latitude and altitude, season, cloud cover and pollution, and time of day.
Dr. Holick, one of the foremost experts on the relationship between vitamin D and human health, was the first to identify the mechanism that allows your skin to synthesize vitamin D. When using sunlight exposure to to increase the amount of vitamin D in your body, Holick recommends staying outside sunscreenless for about half the time it typically takes for you to get a mild sunburn. Another way to gauge when you’ve given your skin enough sun time is to look for the moment when it begins to turn a very light shade of pink.
Especially if you have darker skin, those markers may not work well for you. You may want to rely on the guidelines proposed by vitamin D experts at the National Institutes of Health (NIH), who recommend 5-30 minutes of sun exposure 2 to 3 times a week without sunscreen.