Vitamin D Deficiency: What It Is, and What to Do About It
Do you spend most of your time indoors, slather on sunscreen before going outside, or live in the northern half of the United States? If you answered yes to any of these questions, then it is very likely that you are deficient in vitamin D!
Vitamin D is a unique nutrient that influences our health in many ways – it promotes strong bones, regulates the immune system, and balances hormones – just to name a few effects. Vitamin D deficiency impairs musculoskeletal, immune, and hormonal function and is associated with many chronic diseases.
Read on to learn about the importance of vitamin D for your immunological and hormonal health, and what you can do to correct a deficiency and ensure optimal vitamin D status.
What Is Vitamin D?
Vitamin D is a nutrient with hormone-like properties. The primary sources of vitamin D are sunlight, diet, and supplementation. UVB sunlight exposure has, historically, been the primary source of vitamin D for humans. Sun exposure produces vitamin D via the following steps:
When UVB light rays from the sun hit the skin, a compound in the skin called 7-dehydrocholesterol is transformed into previtamin D3.
Previtamin D3 binds to proteins in the blood and is transported to the liver, where it is turned into 25-hydroxy vitamin D. 25-hydroxy vitamin D is the form of vitamin D measured in blood tests.
25-hydroxy vitamin D is circulated to your tissues, where it is converted into the active form of the vitamin, 1,25-dihydroxy vitamin D. 1,25-dihydroxy vitamin D binds to vitamin D receptors (VDRs) in your body tissues, inducing the beneficial physiological effects of the vitamin.
Compared to sun exposure, foods offer a minimal supply of vitamin D. Foods that naturally contain the vitamin include fatty fish such as salmon, egg yolks, beef, and cod liver oil. For people who don't get much sun exposure and don't eat the foods mentioned above, supplementation may represent their only source of vitamin D.
Why Is Vitamin D Deficiency So Common?
Vitamin D deficiency has been declared an epidemic by public health authorities. According to recent estimates, over a billion people worldwide are vitamin D deficient or insufficient (1).
Why is vitamin D deficiency so common?
Humans evolved in an equatorial environment with abundant sun exposure, making us biologically inclined to obtain much of our vitamin D from sun exposure. In the modern-day world, we spend most of our lives indoors, severely limiting our ability to make vitamin D naturally.
Furthermore, many of us slather on sunscreen before heading outside; sunscreen blocks UVB rays and further limits our skin's ability to produce vitamin D.
Finally, it is difficult to obtain sufficient vitamin D from foods – even fortified foods. Because of these converging factors, vitamin D deficiency has become widespread in modern society, with significant implications for our health.
Vitamin D: a Hormone that Affects the Entire Body
The liver and kidneys activate vitamin D, producing 1,25-dihydroxy vitamin D. Once activated, vitamin D functions as a hormone, interacting with vitamin D receptors to regulate calcium homeostasis and many other physiological functions.
1) Immunity and Vitamin D Deficiency
Vitamin D plays a critical role in regulating the immune system. VDRs (vitamin D receptors) are expressed on B cells, T cells, and antigen-presenting cells, which are immunologic cells that control innate and adaptive immune responses (2).
Vitamin D deficiency is associated with an increased risk of autoimmunity and supplementation with vitamin D may benefit people with autoimmune diseases (3).
2) Blood Sugar Control and Vitamin D Deficiency
Evidence suggests that there is a relationship between vitamin D status and glucose homeostasis. Vitamin D deficiency impairs insulin synthesis and secretion and may promote the development of hyperglycemia, insulin resistance, and type 2 diabetes.
The research on the effectiveness of vitamin D for modulating blood sugar is, however, quite mixed. One study found that vitamin D supplementation significantly improved insulin resistance in type 2 diabetics whereas a meta-analysis determined that vitamin D has no effect on insulin resistance in prediabetic and diabetic individuals. (4, 5)
However, it is possible that the dosages of vitamin D used in these studies were insufficient. Furthermore, the presence of VDR (vitamin D receptor) polymorphisms, leaky gut, excess body fat, or magnesium deficiency in the subjects could have further confounded the results, as these variables necessitate higher doses of vitamin D to achieve therapeutic benefits.
3) Heart Health and Vitamin D Deficiency
Vitamin D is intimately involved in heart health. Numerous animal and human studies indicate that vitamin D deficiency increases the risk of cardiovascular disease (6). Vitamin D may reduce cardiovascular disease risk by normalizing insulin resistance, quenching inflammation, and reducing high blood pressure, all of which are established contributors in the pathogenesis of heart disease.
4) Brain Health and Vitamin D Deficiency
Do you suffer from brain fog, poor memory and concentration, depression, or anxiety? If you answered yes, then you may need more vitamin D! Low vitamin D is linked to poor cognition, depression, and an increased risk of neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases (7, 8, 9).
5) Hormonal Balance and Vitamin D Deficiency
Vitamin D helps regulate the body’s complex hormonal milieu. There is a significant relationship between vitamin D deficiency and hypothyroidism; the greater the deficiency, the more severe the hypothyroid condition (10). Optimal thyroid function may require serum vitamin D levels greater than 125 nmol/L or 50 ng/ml (11).
Research suggests that vitamin D also affects female reproductive hormones. Between 67 and 85 percent of women with PCOS have vitamin D deficiency; low vitamin D levels are associated with insulin resistance, ovulatory and menstrual irregularities, and hyperandrogenism in this population (12). Low vitamin D levels may also contribute to premenstrual syndrome, endometriosis, and female infertility and raise a woman’s risk of breast cancer (13, 14, 15, 16).
If you suffer from hypothyroidism or other hormonal imbalances, I urge you to get your vitamin D levels checked! Replenishing your vitamin D levels may be just the thing your body needs to bring your hormones back into balance!
Testing for Vitamin D Deficiency
It is always wise to check your status of a specific nutrient, such as vitamin D, before beginning supplementation. When you have your vitamin D level measured, the test should look at 25-hydroxyvitamin D, not 1,25-hydroxy vitamin D.
25-hydroxy vitamin D is a prohormone produced by the metabolism of vitamin D in the liver; it is subsequently converted to 1,25-hydroxy vitamin D in the kidneys. While 1,25-hydroxy vitamin D is the most active form of vitamin D in the body, its level in the serum does not accurately reflect the body's true level of vitamin D because it is a short-lived compound. This is why 25-hydroxy vitamin D remains the best indicator of vitamin D status.
You can order your own vitamin D test through YourLabWork. Select “CBC” under the General Health Screening tab and then add vitamin D to the nutrient panel. The vitamin D test costs $80.
Once you begin supplementing with vitamin D, I recommend you re-check your levels every 3 months. If your vitamin D level remains low despite supplementation, you may need to increase your dosage, supplement with magnesium, or improve your gut health to better facilitate nutrient absorption; I cover these topics in more depth below.
Now that you know how to get your vitamin D tested, what is the optimal range for vitamin D? This is a contentious topic that has been widely debated in medical circles. Keep reading to learn what the latest research has to say about what constitutes an optimal vitamin D level!
How Much Vitamin D Do I Need?
For years, Americans have been advised to consume the Recommended Dietary Allowance (RDA) for vitamin D, which corresponds to 600 IU per day for those aged 1-70 years and 800 IU per day for those older than 70.
For reference, the RDA is the “average daily level of intake sufficient to meet the nutrient requirements of nearly all healthy individuals” (17). Vitamin D intakes at these levels roughly produce a serum vitamin D level of 20 ng/ml.
Alarmingly, a growing body of research indicates that these RDA-based intakes are wholly insufficient for the maintenance of optimal health. In fact, the RDA calculations have recently come under scrutiny and been criticized for using faulty statistics, with some researchers arguing that the RDA recommendations are a mere one-tenth of those needed to prevent chronic diseases such as autoimmune and cardiovascular disease (18). The public health and clinical implications of the miscalculated vitamin D RDAs are significant.
In fact, many people are unknowingly suffering the effects of vitamin D deficiency, despite their lab work indicating vitamin D levels in the so-called “normal” range!
If the RDA for vitamin D is inadequate, then what constitutes the optimal blood level of vitamin D needed to prevent chronic diseases? Well, we have several lines of evidence that can help answer this question.
In the largest meta-analysis of vitamin D studies to-date, serum 25-hydroxyvitamin D levels less than 75 nmol/L (30 ng/mL) were associated with increased all-cause mortality and subsequently deemed “too low for safety” (19).
According to the conventional vitamin D reference range, a level of 30 ng/ml is considered “adequate” and it is only when levels reach 12 ng/ml or lower that deficiency is diagnosed! Clearly, our reference range for vitamin D needs some updating!
Fortunately, the functional medicine community has taken this problem into their own hands; functional medicine practitioners routinely recommend patients achieve a serum vitamin D level between 40 and 60 ng/ml. This finding is supported by scientific evidence.
According to rigorous research, serum vitamin D levels of 100 nmol/L (40 ng/mL) or higher are needed to reduce all-cause mortality and proffer benefits to the musculoskeletal, immune, gastrointestinal, cardiovascular, and neurological systems.
What dosage of supplemental vitamin D is required to achieve a serum vitamin D level of at least 40 ng/ml? The Vitamin D Council recommends the following intakes of supplemental vitamin D for achieving a serum level of at least 40 ng/ml:
1000 IU for children aged 1 year or younger
1000 IU per 25 lbs for children 1 year of age and older
5000 IU per day for adults (18 and up)
5000 IU per day for adults 71 years of age and up
Importantly, an individual’s optimal dosage of vitamin D should be refined based on their unique health situation. People living above 37 degrees north or below 37 degrees south latitude, those with gastrointestinal issues (and subsequent nutrient malabsorption), excess body fat, or polymorphisms in VDR (vitamin D receptor) genes may need higher intakes of supplemental vitamin D to achieve optimal serum levels of this crucial nutrient.
Vitamin D does not work in isolation in the body; it functions synergistically with other nutrients, including magnesium and vitamin K2.
Magnesium is a cofactor for enzymes that convert inactive vitamin D into its active form in the liver and kidneys; without sufficient magnesium, vitamin D can’t be metabolized properly and may even lead to improper handling of calcium and subsequent vascular calcification (20).
According to a recent study published in The American Journal of Therapeutics, "…taking large doses of vitamin D can induce severe depletion [of magnesium]. Adequate magnesium supplementation should be considered an important aspect of vitamin D therapy" (21). Focus on eating plenty of magnesium-rich foods, such as dark leafy greens, almonds, pumpkin seeds, dark chocolate, and avocados, and consider whether you may be low in magnesium.
Vitamin K2 also influences vitamin D metabolism. Vitamin K2 is distinct from vitamin K1, the vitamin involved in blood clotting. K2 is found in natto, goose liver, cheese, egg yolks, dark chicken meat, and pastured butter. The ingestion of high doses of vitamin D without concurrent vitamin K2 supplementation leads to vitamin K2 deficiency and may cause dysregulation of calcium homeostasis, leading to calcification of blood vessels and kidney stones.
A vitamin D deficiency is one health problem you don’t want to ignore! Whether you are struggling with autoimmunity, hormonal imbalances, blood sugar dysregulation, or brain fog, vitamin D may be able to help you!
Since it is difficult to obtain sufficient vitamin D from sunlight and food, I recommend that most people supplement. My favorite vitamin D supplement is Designs for Health’s Vitamin D Supreme; it contains vitamin D and vitamin K in optimal proportions, with one capsule delivering 5,000 IU of vitamin D and 550 mcg of vitamins K1 and K2.
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Now, I’d love to hear your thoughts! When was the last time you had your vitamin D level checked? Has correcting a vitamin D deficiency improved your health? Let me know in the comments below.