Introduction

Vitamin D, often referred to as the "sunshine vitamin," is a crucial component for maintaining optimal health and research into its benefits has exploded in recent years. Despite its many benefits, an estimated 42% of American adults are deficient, largely due to lack of sunlight exposure (1). In this article, we discuss the importance of vitamin D, its different forms and sources, and challenges to obtaining it. We’ll explore factors influencing vitamin D deficiency and strategies to mitigate these risks. We’ll also discuss the current recommended daily allowance (RDA) and why researchers believe this value to be outdated.

Vitamin D Overview

Although termed a “vitamin,” vitamin D acts more like a hormone because it can be synthesized within the body through exposure to sunlight unlike most vitamins that are primarily obtained from dietary sources (2). It is primarily synthesized from the sun, but can also be obtained from dietary supplements and, in lesser amounts, from food. The two main forms of vitamin D, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), differ in their source and their effectiveness at maintaining blood levels of vitamin D (3). Vitamin D2 is found in some plant-based sources like mushrooms and fortified foods and is synthesized in fungi and plants when exposed to UVB radiation. Vitamin D3, on the other hand, is present in some animal-based sources like fatty fish, liver, and egg yolks, and is synthesized by the body when exposed to UVB radiation from the sun. Vitamin D3 is more bioavailable and is often considered more effective in raising and maintaining blood levels of vitamin D compared to vitamin D2. Vitamin D3 is therefore the preferred form as it is the form naturally produced in the body and has higher bioavailability. Vitamin D3 can be found in the plant-based essentials, our all-in-one vegan multivitamin.

Functions of Vitamin D

Vitamin D has a range of important functions across multiple systems including regulating calcium and phosphorous absorption to help maintain bone health. Vitamin D also provides immune, cardiovascular, endocrine, and neural support.

Bone Health

Vitamin D enhances the absorption of calcium in the intestines, which is an essential mineral for bone growth. Vitamin D is therefore pivotal in lowering the risk of fractures and in preventing conditions like osteoporosis (4).

Immune System Support

Beyond its role in bone health, vitamin D exhibits immune system benefits, potentially reducing the risk of infections and inflammation (5). Research supports that there’s a correlation between vitamin D deficiency and an increased risk of infection and autoimmune diseases (6). In addition, with the recent COVID-19 pandemic, newer studies have shown that critical COVID-19 patients had lower vitamin D levels than non-critical patients (7), furthering the relationship between vitamin D and the immune system.

Cardiovascular Health

Other research suggests a connection between vitamin D and cardiovascular health, with low vitamin D levels being linked to an increased risk of high blood pressure, heart disease, and stroke (8).

Neural Support

Vitamin D receptors are present in areas of the brain associated with mood regulation, and some studies suggest a link between vitamin D deficiency and an increased risk of depression (9). There have also been correlations between low vitamin D levels, postpartum depression (PPD), and poor sleep quality during pregnancy, though further studies are needed to validate this correlation (10).

Challenges to the Recommended Daily Allowance (RDA)

The current recommended daily allowance (RDA) for vitamin D has faced scrutiny from various scientific studies with multiple review papers supporting that the RDA of 600 IU for adults is a result of a statistical error and should actually be much higher (11). Research indicates that 600 IU for adults is not sufficient to increase serum levels of vitamin D (12). One review supports that an RDA of around 8000 IU is needed to increase serum levels enough to prevent vitamin D deficiency, though the precise amount needed for each individual can be dependent on factors such as sun exposure, age, skin color, and body weight (13).

Factors that Influence Vitamin D Deficiency

There are a few factors that can influence the risk of vitamin D deficiency, including:

Skin Color: Melanin, the pigment responsible for skin color, can impact the efficiency of vitamin D synthesis as melanin blocks the sun’s UVB rays. Individuals with more melanin/darker skin may therefore require more sunlight exposure to produce equal amounts of vitamin D as someone with less melanin (14).

Latitude and Sun Exposure: Geographical location influences the availability to synthesize vitamin D from sunlight, thus impacting vitamin D production. In the winter, those living above or below the 33° latitude are at a high risk of vitamin D deficiency because little to no vitamin D can be produced in the body from the sun (15).

Sunscreen: Sunscreen use blocks UVB rays, which are needed for vitamin D synthesis. Studies show that sunscreen with an SPF of 50 can reduce vitamin D synthesis, though this only has a minimal effect on reducing circulating vitamin D levels (16).

Air Pollution: Emerging evidence suggests a correlation between air pollution and decreased vitamin D synthesis, highlighting yet another environmental factor affecting our health. Higher levels of air pollution reduces the amount of solar UVB that reaches the earth, which results in lower vitamin D synthesis by the body (17).

Age: Vitamin D deficiency is more prevalent in older adults as the skin’s ability to produce vitamin D decreases with age. A recent study showed that between 40%-80% of the older population struggle with vitamin D deficiency (18).

Mitigating Deficiency

The most common ways to mitigate vitamin D deficiency include:

Increasing Sun Exposure: While balancing the amount of time we spend in the sun is important to avoid any harmful effects, increasing sun exposure is the easiest way to mitigate vitamin D deficiency as sunlight is a primary source for vitamin D synthesis. Spending some time outside during peak sunlight hours (midday) can be more effective.

Supplementation: In cases where sun exposure is challenging or not feasible, vitamin D supplementation is a great way to increase vitamin D levels. Consider supplementing with vitamin D that has more than 100% of the RDA and uses D3, the more bioavailable form of vitamin D. In our vegan multivitamin, The Plant-Based Essentials, we use the most effective and bioavailable form of vitamin D, vitamin D3, from a plant-based source (lichen). Keep in mind that most vitamin D3 supplements are made from lanolin, which is extracted from sheep's wool. If following a vegan or plant-based diet, ensure that the source of vitamin D3 is a lichen-derived source. Click here if you're looking for a plant-based vitamin D3 supplement.

Focus on Dietary Sources of Vitamin D: Fatty fish, dairy, egg yolks, and fortified foods are valuable sources of vitamin D. Keep in mind that dietary intake alone may not be sufficient to meet optimal levels.

Monitor Vitamin D Levels: Regular testing ensures that individuals can track their vitamin D status, allowing for adjustments in dietary and lifestyle choices accordingly. Ask for a blood test to measure levels of 25-hydroxy-vitamin D, the circulating form of vitamin D3.

Read more about the best time to supplement with vitamin D here.

Conclusion

Vitamin D has emerged as a powerhouse with diverse functions impacting bone health, the immune system, cardiovascular well-being, and neural support. Vitamin D is synthesized by the body after sunlight exposure, but can also be obtained from supplementation as well as a limited group of foods. The existing RDAs may fall short in capturing the proper recommended daily intake, necessitating a closer look at optimal vitamin D levels. Understanding the factors influencing deficiency and the importance of maintaining vitamin D levels allows for proactive measures against deficiency and can ensure maximal benefits from vitamin D.

References 

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