Vitamin D deficiency and insufficiency are global problems12The survey results revealed a high prevalence of serum 25(OH)D deficiency and insufficiency in the 0-17 year age group, with prevalence rates of 21.4% and 31.0%, respectively, highlighting the high prevalence of these problems in children. Furthermore, serum 25(OH)D levels vary widely with age, sex, and season.
Serum 25(OH)D concentrations vary across countries and regions, with deficiency and insufficiency also affected by differences in sun exposure. In China, median vitamin D concentrations generally follow a north-south gradient, with people in southern provinces such as Hainan, Guangdong, and Guangxi having higher 25(OH)D concentrations than people in northern provinces.19The median serum 25(OH)D concentration was highest in the southernmost Hainan province and lowest in the northernmost Qinghai province.19In contrast, many northern provinces, including Heilongjiang, Jilin, Liaoning, and Inner Mongolia, have 25(OH)D levels that exceed those observed in many central provinces.19.
Our study on the effect of age on vitamin D revealed that serum 25(OH)D concentrations in children aged 0-17 years in Wujiang District, Suzhou City decreased significantly with age. In particular, the proportion of people with serum 25(OH)D concentrations below 30 ng/mL exceeded 60% in the preschool and postschool age groups, reaching 90% in adolescents. Previous studies on vitamin D deficiency in American children showed that the incidence of vitamin D deficiency and insufficiency increased with age, reaching 14%, 20%, and 28.8% in 2-5 year olds, 6-11 year olds, and adolescents, respectively.20,21A study conducted in Harbin, northeastern China, found that among children aged 0-12 years, vitamin D levels in early childhood were significantly higher than those in preschool and school age.twenty twoThe prevalence of vitamin D deficiency among children at different stages in Harbin was lower than that in southeastern China.twenty twoIn a Huzhou-based study, 23.28% of children had low vitamin D levels (< 30 ng/mL) and 6.43% were vitamin D deficient (< 20 ng/mL).twenty threeIn a Wuxi-based study, the prevalence of vitamin D deficiency (<20 ng/mL) in preschool children (3-6 years old) was 48.1%, higher than 21.2% in the toddler group (1-3 years old) and 17.9% in the infant group (0-1 year old).twenty fourThe prevalence of vitamin D insufficiency and deficiency increases significantly from age 1 onwards and with age.twenty threeOverall, our study is consistent with previous studies on vitamin D. However, the vitamin D level adequacy rate among children in this region is only 47.5%, and the levels of vitamin D deficiency and insufficiency are relatively high. Furthermore, logistic regression analysis showed a continuous significant decrease in vitamin D deficiency/insufficiency with increasing age from 1 to 17 years of age. This region is located at a low latitude, receives abundant sunlight throughout the year, and has a relatively higher economic status than other regions in China. The finding of vitamin D deficiency in this region suggests that parents in the local community may not pay enough attention to vitamin D supplementation for their children. Furthermore, as children get older, the occurrence of vitamin D deficiency and insufficiency gradually increases, especially after school age. Given this observation, we encourage parents to follow the recommendation of the Chinese Society of Nutrition, which recommends daily vitamin D supplementation of 400 IU from birth to age 50.twenty five.
Furthermore, during infancy, serum 25(OH)D adequacy reached 71.4%. Although some infants may experience vitamin D deficiency or insufficiency, vitamin D plays an important role in bone development, immune system regulation, cell differentiation, and overall growth during infancy.7Maintaining adequate levels of Vitamin D promotes an infant’s overall health and development and reduces the risk of certain chronic and infectious diseases. Therefore, ensuring adequate Vitamin D intake during infancy is essential to prevent associated health problems.1,26,27Furthermore, our study found that the prevalence of vitamin D deficiency and insufficiency was highest during the winter months in this region, a finding that has been reported in previous studies.28,29However, some studies have shown that vitamin D levels increase gradually in spring and autumn and peak in summer, which differs from our findings, in which peak levels were observed in autumn.22,26Although the results showed a peak in autumn, logistic regression analysis revealed that the risk of vitamin D deficiency/insufficiency was lowest in summer. The prevalence of vitamin D deficiency and insufficiency is lowest in autumn in this region. This phenomenon may be due to the reduction in outdoor activity caused by the heat of summer in this region. Conversely, in autumn, the temperature drops slightly, and children engage in more outdoor activities and have more exposure to sunlight, which affects vitamin D levels. Therefore, it is recommended to consider adequate vitamin D supplementation, especially in winter when sunlight is insufficient and outdoor time is reduced.
Regarding gender differences in vitamin D levels, our study found significant differences between men and women. Previous studies have also shown gender differences in vitamin D. However, our results showed that the median vitamin D level in boys was 1.24 ng/mL higher than that in girls. Furthermore, logistic regression analysis based on girls showed that boys had a lower risk of vitamin D deficiency/insufficiency. Another study found that in a Chinese population, vitamin D levels in men were higher than women, ranging from 2.32 to 4.86 ng/mL.30,31Similarly, studies from South Korea and the United States documented lower mean concentrations of 25(OH)D and higher rates of vitamin D deficiency in women.32,33However, the opposite trends were reported in Italy and Denmark.34,35Studies conducted in Germany and Sweden reported no significant differences in vitamin D levels between men and women.13,36Similarly, the aforementioned differences in vitamin D levels between boys and girls were also confirmed in a study of Chinese children.22,24,37,38Therefore, we speculate that gender differences in vitamin D levels are more likely to be due to different lifestyles, including dietary patterns and time spent outdoors, rather than innate biological differences.
Many factors affect vitamin D levels in children, including environmental, behavioral, and physiological factors. Our findings show that the prevalence of vitamin D deficiency (<20 ng/mL) in Chinese children aged 0-17 years increases with age. This observation may be due to the Chinese Pediatric Society's recommendation that all children should receive at least 400 IU of vitamin D per day from birth to 2 years of age.twenty fiveThe body’s vitamin D conversion process involves the synthesis of previtamin D3 through the skin when exposed to ultraviolet rays, which is then converted to 25-hydroxyvitamin D3 by the action of dehydrogenase in the liver. However, for children over the age of 2, the main source of vitamin D is outdoor activity. Research has shown that children’s vitamin D levels are low due to limited outdoor activity.38,39,40Based on our findings and previous research, and with a better understanding of children’s health, we recognize that the situation of vitamin D insufficiency and deficiency in this region is relatively serious. Considering the important role of vitamin D levels in children’s growth and overall health, we propose an initiative to supplement children’s vitamin D intake. This initiative aims to ensure that children receive sufficient vitamin D support for their health.
The present study has notable strengths, collecting serum 25(OH)D from 11,116 children aged 0–17 years in Wujiang District, Suzhou City, southeastern China, from 2020 to 2023, providing a substantial sample size. Furthermore, we assessed vitamin D levels across different age groups (0–17 years), providing valuable insights into serum 25(OH)D status based on various factors such as gender, age, season, and province in this region. However, it is important to acknowledge that the present study has some limitations. We did not extensively capture children’s sociodemographic characteristics and lifestyle factors that may affect serum 25(OH)D concentrations, such as vitamin D supplementation, time spent in outdoor activities, and BMI. Nevertheless, the study population consisted of 11,116 children undergoing regular health checkups at the hospital, increasing the representativeness of participants in the local child population. Further studies are needed to explore potential factors and variables associated with vitamin D status.41.
