Vitamin D deficiency has many adverse clinical consequences, including poor musculoskeletal health, manifesting as diseases like rickets and osteomalacia. Moreover, vitamin D may be crucial for preventing extra skeletal diseases like cancer and diabetes.
Vitamin D is biologically inactive in the human body; thus, in laboratory detection of vitamin D deficiency, they measure serum concentrations of 25-hydroxyvitamin D (25(OH)D), a vitamin D metabolite utilized by the body and that reflects the overall supply from different sources, including ultraviolet-B (sunlight) and food sources, such as fish or mushrooms.
Worldwide, the prevalence of low serum levels of 25(OH)D, i.e., below 25-30 nmol/L and 50 nmol/L, occurs in ~5-18% and 24-49% of people, respectively, underscoring the need for prompt action to reduce vitamin D deficiency burden globally. At a dosage of 50µg per day, the whole 25(OH)D distribution of a given population could rise to higher levels; however, there are safety concerns with such dosage as it may also increase the risk of vitamin D overdosing for those at the higher end of the distribution.
Moreover, given the extra skeletal health effects of vitamin D, it is crucial to focus on the attainment of 25(OH)D levels needed to prevent them rather than safety concerns for targeting 75 nmol/L (30 ng/mL), which are optimal target serum 25(OH)D concentrations for skeletal health. So, researchers additionally investigated whether attaining serum 25(OH)D levels ≥50 nmol/L should be the target.
Guidelines for vitamin D intake establish target serum 25(OH)D concentrations and recommend the required doses to achieve those levels, assuming adequate intake of other nutrients and seasons (winters or summers).
Accordingly, current guidelines recommend a daily vitamin D intake of 400-800 IU; however, individuals from different ethnicities or regions may require even higher intakes of 2008-2672 IUs for attaining 25(OH)D serum levels of ≥50 nmol/L.
What should be the target serum 25(OH)D levels: 75 nmol/L (30 ng/mL) or 2000 IU (50 µg)?
Many observational studies have suggested that while ≥50 nmol/L serum 25(OH)D levels can prevent rickets and osteomalacia, concentrations ≥75 nmol/L are needed for improved health outcomes in diabetes and cancer.
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The optimal concentration needed may also vary depending on the study population and outcome of interest. Further, the authors noted that randomized controlled trials (RCTs) testing 25(OH)D needs may be biased towards healthy people who may not accurately represent the general population, especially those with obesity.
In fact, optimal serum 25(OH)D concentrations for most chronic diseases are slightly above 75 nmol/L (30 ng/mL). Thus, obese individuals, individuals with higher body mass index (BMI), and patients with malabsorption syndromes may require higher doses of vitamin D to increase their serum 25(OH)D levels.
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