By Dr. John Neustadt

It’s been a hundred years since the first paper on vitamin D was published. In their research into the underlying causes of rickets, researchers in 1922 suggested that vitamin D promoted calcium deposition in bones.¹ Since then, researchers discovered that without vitamin D, only about 15% of dietary calcium and 60% of phosphorus are absorbed. On the other hand, with enough vitamin D calcium absorption increases by up to 40% and phosphorus absorption increases by 80%.² 

But those are only a couple of the dozens of health effects researchers have uncovered. Beyond bone health and vitamin D’s effects on calcium and phosphorous, some surprising benefits of Vitamin D include supporting:³

• Healthy muscle mass and strength
• Balance
• Immune system health
• Skin health
• Brain health
• Cellular health
• Intestinal health
• Lung health
• Heart health
• Neurological health

Vitamin D is an incredibly popular dietary supplement, and many people know they should take it. But how much should you take and does genetics play a role? 

Genetic vs Environment

About 3% of human genes are directly or indirectly controlled by vitamin D and its metabolites.³ Vitamin D regulates the functions of more than 200 genes and is one of the most important molecules for your health—so important that the human body produces its own supply daily from the ultraviolet B (UVB) spectrum of sunlight.⁴ 

Despite the important role vitamin D plays in genetics, there’s little or no evidence that your genes—instead of environmental factors—governs your vitamin D levels.^5,6 Skin pigmentation, sunscreen, exposing less skin to the sun, aging, time of day, season, latitude and altitude all affect vitamin D levels.⁷ People at particularly high risk for not getting enough vitamin D include pregnant women, people of color (blacks, Hispanics and anyone with increased skin melanin pigmentation), obese children and adults and children and adults who avoid direct sun exposure, people with malabsorption conditions (eg, leaky gut, Celiac disease, Crohn’s disease), diabetes and people taking medications that reduce vitamin D levels (eg, anticonvulsants, systemic glucocorticoids, ketoconazole, or antiretrovirals).^1,8  

To prevent Vitamin D deficiency, it takes fifteen to twenty minutes of sunshine daily with more than 40% of your skin exposed.⁴ However, most people aren’t getting enough direct sun exposure—even in the summer—to produce enough vitamin D.⁹ 

Your Blood Vitamin D Level

There is no worldwide consensus regarding the cutoff value for definition of vitamin D deficiency or how much someone should take for optimal health. Typically, vitamin D deficiency is defined as a 25(OH)D level of less than 20 nanograms per milliliter (ng/mL), with severe deficiency defined as less than 10 ng/m and insufficiency between 20 and 30 ng/mL.¹⁰ 

However, the Endocrine Society reviewed the research and concluded that the healthy range for serum vitamin D is 30-100 ng/mL. Interestingly, this recommendation most closely approximates vitamin D levels obtained by natural sunlight exposure. Serum vitamin D levels as a result of exposure to sunshine can be as high as 90 ng/mL.¹¹ Similarly, outdoor workers who are routinely exposed to sunshine have vitamin D levels within this range. The vitamin D levels in farmers and lifeguards have been shown to be 54 ng/mL and 65 ng/mL, respectively.¹²

How Much Should You Take?

According to a 2020 review, “There is lack of consensus as to the optimal level and no unanimity as to the dose.”¹¹ Given that, how does a person decide? 

While the Endocrine Society concluded a healthy vitamin D blood level is 30-100 ng/mL, that’s a big range. Is there an optimal amount? Studies have evaluated this question. Based on clinical trials and meta-analyses, the optimal range appears to be about 50-60 ng/mL.^13,14 

In studies using different amounts of vitamin D3, most healthy adults reached 30-44 ng/mL when taking 1,800 to 4,000 IU vitamin D3 for at least 42 days.¹³  Multiple studies have concluded that vitamin D levels increase by about 1 ng/mL for every 2.5 mcg (100 IU) of vitamin D3.^15,16 Therefore, to get vitamin D into the optimal range of 50-60 ng/mL, people may need to take vitamin D3 125 mcg (5,000 IU) or more per day, which is what NBI’s Vitamin D3 provides. 

How Long Should You Take It?

Studies have shown it takes about five to six months to reach a steady state, at which point your vitamin D levels remain fairly constant.¹⁷ During that time, many clinicians recommend testing your vitamin D levels every three months to make sure you’re vitamin D is moving toward an optimal level and whether you need to adjust the amount you’re taking. 

Vitamin D Safety

More than 20 publications concluded that there was no association between harm and intakes of 250 mcg (10,000 IU) per day.^12,13,18,19 In fact, an expert committee of the Food and Nutrition Board at the US National Academies of Sciences, Engineering and Medicine (NASEM) concluded that toxicity is unlikely at intakes below 250 mcg (10,000 IU) daily.²⁰

 While it’s important to work with your healthcare provider to determine the optimal dose and blood levels for you, Vitamin D toxicity doesn’t generally occur until serum vitamin D levels reach 100–150 ng/mL.^21,22

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