Vitamin D in the Dietary Reference Intakes for Japanese (DRIs) 2020

Vitamin D insufficiency and disease risk in the elderly

Vitamin D insufficiency, milder than deficiency, is common, and a risk of various diseases. Since vitamin D exert diverse actions, both skeletal and non-skeletal, its insufficiency is a risk of various diseases including osteoporosis, sarcopenia, cardiovascular disease, cancer, and even mortality. Regarding the association of vitamin D status and disease risk, a marked discrepancy exists between the results from the observational studies and intervention studies, mostly yielding the positive and negative results in the former and latter, respectively. Such inconsistency probably arises from methodological problems, of which the baseline vitamin D status would be the most important. Vitamin D intervention would be effective in the deficient/insufficient subjects, but not in sufficient subjects. Since the elderly subjects, especially the institutionalized people, are mostly vitamin D deficient/insufficient, they are likely to benefit from improvement of vitamin D status. Vitamin insufficiency is a risk of various diseases, and correcting the vitamin status alone would reduce the risk of many diseases, and favorable to avoid the undesirable consequences of polypharmacy in the elderly. Additionally, disease prevention by nutritional improvement is cheap and free from side effects, and suited for the primary prevention of diseases.

Determination of a Serum 25-Hydroxyvitamin D Reference Ranges in Japanese Adults Using Fully Automated Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

Despite an increasing interest in vitamin D status, a reference range of the nutrient has not been fully established. This is partly due to a paucity of standardized measuring systems with high throughput. In addition, the range may vary by populations and may change with modernization of lifestyles.

OBJECTIVES

This study aims to calculate the current reference concentration of 25-hydroxyvitamin D (25(OH)D) among healthy people living in an urban area in Japan.

METHODS

A newly developed fully automated liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) system was used to measure serum 25(OH)D concentrations. Reproducibility was assessed by measuring standardized samples. Accuracy was validated by comparing with commercially available immunoassays. Then, mass screening was conducted targeting participants who received medical checkups in Tokyo from April 2019 to March 2020, and the reference ranges were calculated.

RESULTS

The coefficients of variations of interoperator and interday reproducibility were 4.1%-8.5% and 3.7%-8.0% for 25-hydroxyvitamin D₂ (25(OH)D2) and 4.7%-7.0% and 4.0%-6.9% for 25-hydroxyvitamine D3, respectively. The measured total 25(OH)D concentrations correlated well with those measured by immunoassays. In total, 5518 participants were measured for 25(OH)D concentrations, among whom 98% showed inadequate concentrations (<30 ng/mL). The reference ranges of total 25(OH)D for female, male, and total participants were 7-30 ng/mL, 5-27 ng/mL, and 6-29 ng/mL, respectively. After excluding those with abnormal renal and liver function, the range was 6-30 ng/mL.

CONCLUSIONS

The high prevalence of vitamin D insufficiency among seemingly healthy population may be attributed to lifestyle characteristics of people living in urban areas of Japan, including spending less time outdoors and lower intake of traditional foods. Longitudinal follow-up and mass screenings targeting different population will help elucidate reasons for discrepancies between official guidelines and the observed concentrations, to which the well-validated measurement system is essential.

Breastfeeding and vitamin D

The recent re-emergence of vitamin D deficiency (VDD) and rickets among breastfed infants without adequate sunlight exposure and vitamin D supplementation has been reported worldwide. Breastfed infants are particularly vulnerable to VDD because of the low vitamin D content of breast milk, restricted sunlight exposure, increased pollution, and limited natural dietary sources of vitamin D. The prevalence of VDD in breastfed infants differs vastly between studies and nations at 0.6%-91.1%. The recommended intake of vitamin D for lactating mothers to optimize their overall vitamin D status and, consequently, of their breast milk is 200-2,000 IU/day, indicating a lack of consensus. Some studies have suggested that maternal high-dose vitamin D supplementation (up to 6,400 IU/day) can be used as an alternate strategy to direct infant supplementation. However, concern persists about the safety of maternal high-dose vitamin D supplementation. Direct infant supplementation is the currently available option to support vitamin D status in breastfed infants. The recommended dose for vitamin D supplementation in breastfed infants according to various societies and organizations worldwide is 200-1,200 IU/day. Most international guidelines recommend that exclusively or partially breastfed infants be supplemented with 400 IU/day of vitamin D during their first year of life. However, domestic studies on the status and guidelines for vitamin D in breastfed infants are insufficient. This review summarizes the prevalence of VDD in breastfed infants, vitamin D content of breast milk, and current guidelines for vitamin D supplementation of lactating mothers and infants to prevent VDD in breastfed infants.