Develop Immune Resilience

Do you struggle with frequent colds and infections? Low vitamin D may be the culprit. Research shows there’s a link between low vitamin D levels and respiratory tract infections like the common cold, bronchitis, pneumonia, RSV, COVID-19, and influenza.³ Studies also show that improved vitamin D levels translate to a significant decrease in the risk of developing these types of infections.

So what is the ideal level of vitamin D to prevent viral respiratory illnesses? One study investigated the relationship between declining vitamin D levels seen in the fall and winter and frequency of infections in 198 healthy adults living in New England. Blood levels of vitamin D 38 ng/mL (a common measurement of vitamin D) and higher were associated with a “significant two-fold reduction in the risk of developing acute respiratory tract infections and with a marked reduction in the percentages of days ill.” The researchers also noted that “light skin pigmentation, lean body mass, and supplementation with vitamin D were found to correlate with higher concentrations [of vitamin D].”⁴

Supplementing with vitamin D to achieve this higher level is key. A randomized, double-blind, placebo-controlled trial of school-aged children comparing vitamin D supplements with a placebo and the incidence of influenza, revealed that children who took 1,200 IU of vitamin D daily for four months saw a 42 percent reduction in the risk of getting the flu.⁵ Another randomized, controlled trial of vitamin D supplementation in pregnant women and infants determined that when healthy pregnant women supplemented with 2,000 IU of vitamin D daily, and their infants received 800 IU in the months after birth, the child experienced a significant reduction in the number of acute respiratory infections between six and 18 months of age.⁶

Defend Against Long COVID

Long COVID—which can include neurocognitive, cardiorespiratory, gastrointestinal, musculoskeletal, and taste and smell disorders—is an emerging syndrome affecting 50 to 70 percent of those who contract COVID.⁷

In one recent double-blind, randomized, placebo-controlled trial, patients with post-COVID symptoms saw significant improvements in fatigue, anxiety, and cognitive symptoms after taking 8,500 IU of vitamin D daily for eight weeks compared to the placebo group. The study concluded, “High-dose vitamin D supplementation may benefit patients with post-COVID syndrome by reducing fatigue, alleviating anxiety, and improving cognitive symptoms, with minimal side effects.”⁸

Build Strong Bones & Maintain Oral Health

Vitamin D is essential for strong bones and healthy teeth. It helps the body absorb and retain calcium and phosphorus, which are required for maintaining strong bones, and is positively associated with bone mineral density (BMD).⁹ Vitamin D also reduces the risks of bone fractures.¹⁰ A meta-analysis of 11 randomized, controlled trials involving more than 30,000 adults aged 65 and older, nearly 90 percent of whom had insufficient vitamin D levels, found that vitamin D supplementation (800–2,000 IU daily) reduced the risk of hip fractures by 30 percent and nonvertebral fractures by 14 percent.¹¹

According to a 2023 study in children ages two to 17, serum vitamin D levels below the normal range had twice the risk of experiencing a fracture compared to those with normal vitamin D levels. For each unit increase in serum vitamin D levels, the likelihood of fractures at various locations in the forearm decreased by up to seven percent. Researchers also found that when children with fractures and low vitamin D levels were supplemented with vitamin D and calcium at 2,000 IU and 600 mg per day, respectively, healing improved.¹²

Vitamin D is also essential for oral health in both children and adults. A 2023 meta-analysis of 16 studies found that individuals with periodontitis (gum disease) have lower serum vitamin D levels compared to healthy individuals without periodontitis.¹³

Maintain Muscle Mass & Strength

Vitamin D is also essential for muscle development and repair. It plays a large role in supporting healthy muscle mass and overall muscle function, and low levels of vitamin D are associated with reduced muscle mass and strength. Studies show that supplementing with D improves these parameters.¹⁴

In two randomized, controlled trials of 160 postmenopausal women (aged 50–65 years) with insufficient-to-deficient vitamin D levels (mean serum levels less than 20ng/mL), supplementation with 1,000 IU vitamin D daily for nine months resulted in a lower incidence of falls and improvement in postural balance, and was shown to preserve lean muscle mass and improve muscle strength.¹⁵

Enhance Cognitive Function and Mood

Vitamin D plays an important role in brain development and function.¹⁶ It is necessary for neuronal development, including those neurons involved in learning and memory,¹⁷ and it’s been shown to help kids with attention deficit hyperactivity disorder (ADHD). Studies show that when children with ADHD and vitamin D deficiency were supplemented with 3,000 IU of vitamin D daily for 12 weeks (in addition to receiving standard therapy for ADHD) they saw significant improvements in both inattention and hyperactivity compared to a placebo.¹⁸

Low levels of vitamin D present a real risk for cognitive decline as we age. A 2017 review and meta-analysis showed that vitamin D deficiency (levels less than 10 ng/mL) increases the risk for dementia, especially in adults 65 and older.^{19 20} Optimal levels of vitamin D also provide possible protection against the neurodegenerative processes associated with Alzheimer's disease, including the clearance of amyloid-β plaques, a hallmark of Alzheimer’s.^{21 22}

Another reason to incorporate vitamin D into your daily routine is its mood-boosting and stress-mitigating benefits. A 2021 study investigated the impact of vitamin D deficiency on mental health in university students with eye-opening results. Of the 480 students recruited for the study, 287 (nearly 60 percent) had a vitamin D deficiency. The prevalence of depression, anxiety, and stress among the D-deficient students was 60.35%, 6.31%, and 75.08%, respectively. The odds of developing depression, anxiety, and stress were significantly higher in the vitamin D-deficient individuals. The research showed a strong association between psychological stress and vitamin D deficiency, concluding that, “Controlling vitamin D levels not only helps to control the wide range of psychological burdens but also helps to improve the academic performance of the students.”²³

Vitamin D supplementation has also been shown to positively impact mood and improve depressive symptoms in children. A 2024 randomized, controlled trial found that supplementing school-aged children with 2,000 IU vitamin D daily for nine weeks resulted in significant reductions in depressive symptoms.²⁴

Strengthen Cardiovascular Health

Looking for an easy way to support heart health? Studies show that increasing vitamin D levels through supplementation can reduce the risk of cardiovascular disease (CVD) and stroke by decreasing blood pressure, protecting against arterial stiffness and arterial wall thickening, improving endothelial function, and supporting blood sugar homeostasis, all critical markers of cardiovascular health.^{25 26} A meta-analysis of 34 studies, which included 80,667 participants, found that for every 10 ng/mL increase in serum vitamin D, there was a 10 percent lower risk of cardiovascular events like stroke and heart attack and a 12 percent lower risk of cardiovascular mortality.²⁷

Natural Vitamin D Production and the Factors at Play

Vitamin D is dubbed the “sunshine vitamin” because it’s the only vitamin the human body can produce through exposure to UVB rays; it’s said that we can achieve optimal vitamin D levels just by spending 20 minutes a day in the sun. But, in reality, many factors come into play for this to hold up. The caveat to optimizing natural vitamin D production is that large areas of the skin (arms, legs, face, and abdomen) need to be exposed to the sun—without sunscreen (sunscreen with an SPF of 30 reduces the capacity of the skin to produce vitamin D by 95 to 98 percent).^{28 29} time of day is also important; between 10 a.m. and 4 p.m. provides the strongest UVB rays that lead to sufficient vitamin D synthesis.³⁰ And as already mentioned, the time of year also matters. Age and skin color are also factors. Younger people tend to have better vitamin D production compared to older adults, and those with lighter skin are more efficient at producing vitamin D compared to people with darker skin.^{31 32} Weight is another factor. Individuals with a body mass index (BMI) of 30 or more have been found to generally have lower vitamin D levels and may require more vitamin D to achieve levels of those with normal weight.³³

Other factors that can impact vitamin D production in the body include having adequate magnesium levels, which plays a key role in vitamin D metabolism and absorption, having a healthy liver, which is required to convert vitamin D into its active form, and environmental factors, such as cloud cover, pollution, and altitude, which impact the amount of UVB rays reaching the skin.^{34 35 36 37} Lastly, lifestyle factors, such as working indoors during daylight hours, can also impede vitamin D production. UVB radiation does not penetrate glass, so exposure to sunshine indoors or in a car through a window does not produce vitamin D in the body.³⁸

What Are Optimal Levels?

The Endocrine Society, the National and International Osteoporosis Foundation, and the American Geriatric Society define vitamin D deficiency as vitamin D levels in the blood of less than 30 ng/mL. The Endocrine Society recommends a range of 40–60 ng/mL with a daily intake of 400–1,000 International Units (IU) for infants less than one year, 600–1,000 IU for children and adolescents from 1–18 years, and 1,500–2,000 IU for all adults.³⁹ The best way to know your current vitamin D level is to get tested. The 25-hydroxy vitamin D test measures the amount of vitamin D in your blood so you can get a baseline and go from there.

References

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