Addressing Vitamin D Deficiency

Vitamin D is a critically important nutrient that oversees many aspects of our health. It is commonly known as the sunshine vitamin because the body can produce it after sun exposure. Smaller amounts of vitamin D3 can be obtained from food sources such as oily fish, especially wild caught salmon. Vitamin D2 is added to some foods like milk or milk alternatives like nut milk. However, it is cleared by the body faster than vitamin D3 and therefore not as bioavailable.

Vitamin D3 has taken center stage recently as more and more research is pointing to the many benefits this vitamin has for immune health. Several studies show it can keep the body healthy and strong during modern day immune challenges.^1,2 Some studies have found a relationship between vitamin D deficiency or insufficiency and higher incidence and severity of COVID-19.^1,2 Normal levels are also critical for heart and brain health, staying mobile into old age, avoiding autoimmune issues, multiple sclerosis, and migraines, and many more health benefits.³

Yet, many people have either insufficient or deficient levels of vitamin D. Nearly half of the people in the United States have 25-hydroxyvitamin D [25(OH)D] levels below 20 ng/mL.⁴ This number is even higher for people with darker skin tones.⁴ These low levels leave them vulnerable to poor health. In addition, not everyone absorbs enough vitamin D either from food or supplements, as I’ll discuss later.

This article will discuss the research on the health benefits of vitamin D as well as a way to make vitamin D more bioavailable.

What Causes Vitamin D Deficiency?     

• Where a Person Lives – Living at a northern latitude or in a place where there’s lots of air pollution can reduce the amount of sunlight you’re exposed to even if you spend a lot of time outdoors.⁵ The intensity of UVB radiation is weaker under a cloak of air pollution and in northern latitudes especially in winter.^5,6 In addition, northern latitudes are colder and people spend less time outdoors in the winter.
• Not Spending Enough Time Outdoors – In the modern world, many people have indoor jobs where they rarely get outside during the day. Even on weekends, household chores or indoor shopping keep people away from sunlight. This means exposure to vitamin-D producing UVB radiation is low to non-existent.
• Wearing Sunscreen and Protective Clothing – Even people who spend time outdoors often wear sunscreen, hats, and/or long-sleeved shirts. These block exposure to sunlight and reduce vitamin D production in the body. Applying sunscreen that has a sun protection factor (SPF) of 10 lowers UVB radiation by 90%.⁷
• Having a Dark Complexion – Individuals who have darker skin don’t make as much vitamin D after sun exposure as people with lighter skin.⁸ One study found that average serum 25-hydroxyvitamin D levels were 28.1 ng/mL in Caucasians, 21.6 ng/mL in Mexican Americans, and only 16.9 ng/mL in African American adults.⁹
• Genetic Factors – Some people may have a genetic predisposition to low vitamin D levels. One study of more than 33,000 people of European descent found common variations known as polymorphisms in genes involved in vitamin D transport and cholesterol synthesis.¹⁰ These polymorphisms affected vitamin D levels. Other research unveiled a genetic risk of vitamin D deficiency in individuals of European¹¹, Asian,^12,13 and African¹⁴ descent. In one study, in order to reach optimal vitamin D levels, people with the highest genetic risk of vitamin D deficiency needed an additional 467 to 500 IU of vitamin D per day compared to people with the lowest genetic risk.⁴ These genetic differences can determine how much vitamin D supplementation is needed to bring each individual person up to the optimal levels. Improving the absorption of vitamin D may be particularly useful for people with these genetic variations.
• Old Age – Elderly people’s bodies don’t do as good a job of making vitamin D when exposed to UVB radiation. They’re also more likely to spend more time indoors and use sunscreen when they do go outside. An estimated 44% of elderly men and 26% of elderly women have very severe vitamin D deficiency.³ In one study, only 15% of elderly people had normal serum 25(OH)D levels.³
• Magnesium Deficiency – Having optimal magnesium levels can reduce the risk of vitamin D insufficiency or deficiency.¹⁵ Magnesium governs the activity of important enzymes involved in vitamin D metabolism.¹⁵ This means that magnesium deficiency can lead to lower vitamin D levels.
• Certain Diseases – Chronic kidney disease, inflammatory bowel disease (IBD), cholestatic and non-cholestatic liver diseases, and cystic fibrosis can all cause a drop in vitamin D levels. People with chronic kidney disease don’t make enough 1α,25-dihydroxyvitamin D and they lose a lot of 25-hydroxyvitamin D in their urine.¹⁶ In one study of IBD patients, there was a 33.3% increased prevalence of vitamin D deficiency in Crohn’s disease and 20.3% in people with ulcerative colitis.¹⁷ In Crohn’s disease, vitamin D deficiency was linked to increased disease activity and a higher level of fecal calprotectin, a protein that serves as a marker of inflammation in the gastrointestinal tract.¹⁷ In ulcerative colitis, vitamin D deficiency was also linked to worse disease activity as well as the use of steroids during the last six months.¹⁷ People with cholestatic and non-cholestatic liver diseasesand cystic fibrosis don’t absorb enough vitamin D from the diet and don’t do a good job of converting vitamin D to its active form 25-hydroxyvitamin D.¹⁸
• Obesity – In people whose body mass index is ≥30 kg/m², vitamin D can be stored in body fat deposits.¹⁹ This makes it less useable to the body. Compared to normal weight people with a BMI under 25 kg/m², obese individuals have lower serum 25-hydroxyvitamin D levels after vitamin D supplementation.²⁰

What Are Healthy Vitamin D Levels?

In the United States, serum 25-hydroxyvitamin D concentrations are measured using ng/mL while in Europe nmol/L are used. The US Endocrine Society defines vitamin D deficiency as serum 25-hydroxyvitamin D values ≤20 ng/mL (≤50 nmol/L), insufficiency as serum 25-hydroxyvitamin D values of 21 to 29 ng/mL (51 to 74 nmol/L), and sufficiency as serum 25-hydroxyvitamin D values of 30 to 100 ng/mL (75 to 250 nmol/L). Healthcare practitioners will have their own ideal ranges.

Enhancing the Absorption of Vitamin D

As mentioned earlier, some people don’t absorb vitamin D well, such as those with genetic polymorphisms, obese people, people who are magnesium deficient, or who have certain diseases. In addition, even the acidic pH of gastric juice or high levels of fiber in the diet may impact how well the body absorbs vitamin D.²¹ Furthermore, vitamins E and K share a common pathway as vitamin D for uptake in the intestines.²¹ Therefore, they may compete with vitamin D for absorption. Vitamin A may also block vitamin D absorption.²¹  Additionally, vitamin D is also a fat-soluble nutrient. Taking it with a low-fat meal may therefore reduce its bioavailability.

Because of the many factors that can interfere with the body’s absorption of vitamin D, improving its absorption can have a large impact on health.

Conclusion

Vitamin D is a multi-talented nutrient that is critical for every aspect of health. Unfortunately, many factors leave people depleted of this important vitamin. In addition, many people don’t absorb vitamin D well due to factors like age, obesity, certain diseases, low magnesium intake, and high amounts of vitamin A.

References:

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