Elsevier

Nutrition

Volume 17, Issues 11–12, November 2001, Pages 921-925
Nutrition

Applied nutritional investigation
Low serum concentrations of 25-hydroxyvitamin D in young adult Japanese women: a cross sectional study

https://doi.org/10.1016/S0899-9007(01)00662-1Get rights and content

Abstract

OBJECTIVES: The vitamin D nutrition status of young adult women is unclear, but a recent preliminary report suggested that they may have vitamin D insufficiency. This study assessed the serum concentrations of 25-hydroxyvitamin D (25[OH]D), an index of vitamin D nutrition status, in young adult Japanese women in comparison with those in older women and investigated whether serum 25(OH)D concentrations are associated with other calcium-related hormones and bone mass.

METHODS: A cross sectional study of 77 healthy women, age 19 to 66 y, working in nursing homes in Japan was conducted in the winter of 1999 and 2000. The investigation included blood tests, forearm bone mass measurements, and a lifestyle questionnaire.

RESULTS: The mean serum 25(OH)D concentration in women younger than 30 y was 34.0 nmol/L (standard deviation [SD] = 11.0) and significantly lower than that in women 30 y and older (50.0 nmol/L, SD = 14.4). The proportion of subjects younger than 30 y who had serum 25(OH)D concentrations less than 30 nmol/L was 42.1% and was significantly higher (P < 0.001) than the proportion of those 30 y and older (10.3%). There was a weak but significant linear association between serum 25(OH)D concentrations and forearm bone mineral content (R2 = 0.114, P = 0.0052) but not between serum 25(OH)D concentrations and bone mineral density. The association held after adjusting for body weight (R2 = 0.139, P = 0.0111). Serum intact parathyroid hormone concentrations were within the normal range and not associated with serum 25(OH)D concentrations.

CONCLUSIONS: Serum 25(OH)D concentrations in young adult Japanese women (<30 y old) are lower than those of older adult women (30 to 66 y), and lower serum 25(OH)D concentrations are likely associated with lower forearm bone mineral content.

Introduction

Vitamin D nutrition status, which is most closely reflected by the serum concentration of 25-hydroxyvitamin D (25[OH]D), the stable form of vitamin D metabolized in the liver,1 is a topic currently of interest in relation to bone health. Insufficient serum concentrations of 25(OH)D are thought to lead to secondary hyperparathyroidism, which is a contributing factor to the age-related acceleration of bone loss.2, 3

Vitamin D insufficiency is common in elderly people and seems to be a serious health problem.4 Vitamin D insufficiency in the elderly has been explained mainly by an age-related decrease in serum 25(OH)D concentration, probably resulting from a reduction in vitamin D biosynthesis in the skin.5, 6 Contrary to expectations, low levels of serum 25(OH)D have been recently reported in young women.7 In comparison with the large number of epidemiologic studies on the vitamin D nutrition in elderly women, however, there have been fewer studies in young women.

We reported low serum 25(OH)D concentrations in female Japanese college students,7 but that study was not designed to compare the serum 25(OH)D concentrations of young adult women with those of their older counterparts. Environmental factors such as seasons and occupation (indoor versus outdoor) are important determinants of serum 25(OH)D concentration because of their relation to ultraviolet exposure and may have considerably affected the results of the study. Thus, a better designed epidemiologic study was needed to confirm our preliminary findings.

To address the question of whether young adult women have inadequate vitamin D nutrition status, we studied a wide age range of adult working women in the same setting. The purposes of the present study were to assess the serum 25(OH)D concentrations of young adult Japanese women in comparison with their older counterparts and evaluate the effects of low 25(OH)D concentrations by simultaneously evaluating other calcium-regulating hormones, in particular parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25[OH]2D), and bone mass.

Section snippets

Subjects and methods

We targeted an accessible adult female population—127 healthy women working at three nursing homes in Niigata (latitude 37°48 to 59′N), Japan-and 80 (63.0%), aged 19 to 66 y, agreed to participate in this study. Three of the women were taking vitamin D supplements and were excluded. No subject was taking any sex steroid hormones or medication for osteoporosis. Ultimately, 77 women were included in the analysis. The subjects were engaged in ordinary daytime work, but 39 subjects were also on

Results

The mean age of the subjects was 32.9 y (SD = 11.3), and their mean body weight was 52.0 kg (SD = 6.2). Subjects’ average serum 25(OH)D3 concentration was 42.0 nmol/L (SD = 15.1). Serum 25(OH)D2 was detected in only three subjects (2.1, 2.4, and 3.1 nmol/L). The mean concentration of serum 25(OH)D, the sum of the serum 25(OH)D3 and 25(OH)D2 values, was 42.1 nmol/L (SD = 15.1). The mean serum 25(OH)D concentrations of the 10-y age groups are shown in Fig. 1. The mean serum 25(OH)D

Discussion

The present study clearly demonstrated that the women younger than 30 y had lower serum 25(OH)D concentrations (mean = 34.0 nmol/L) than the women aged 30 to 66 y. This finding conflicts with the current belief that vitamin D nutrition status, i.e., that serum 25(OH)D concentrations decrease with age.5, 6 Moreover, when a serum 25(OH)D concentration cutoff value of 30 nmol/L was adopted, the prevalence of vitamin D insufficiency in women in their 20s was 42.1%, which is close to the rate

Acknowledgements

The authors thank the staffs of the nursing homes Atagonosono, Honaminosato, and Hoseien for their helpful assistance in data collection. They also thank Toyo Medic Inc. for allowing us to use the DTX-200 Osteometer.

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