Maternal and Fetal Effects of Gestational Vitamin D Concentration

Most (90%) vitamin D synthesis occurs in the skin using sunlight (ultraviolet rays), and 10% is obtained through food. Vitamin D is an essential nutrient for skeletal growth and maintenance, cell proliferation and differentiation, and immune function. This study investigated whether maternal serum vitamin D concentrations induce maternofetal effects. Hematological analysis, serological changes, and precision fetal ultrasound findings were analyzed by maternal vitamin D concentration in gestational weeks 22-25 to ascertain direct effects on fetal growth. Bone density-vitamin D concentration correlation was analyzed. No hematologic or serological effect of maternal vitamin D concentration was detected; however, the sexually transmitted infection and cross-infection rates were inversely proportional to maternal vitamin D concentration. No significant correlation between vitamin D concentration and vertebral and femoral BMD was detected. For fetal growth, biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length were analyzed. Humerus (p < 0.05) and femur (p < 0.001) lengths were higher in the vitamin D-sufficient group than in the vitamin D-deficient group. Vitamin D concentration did not positively affect hematologic changes and bone density; maternal vitamin D concentration essentially affected fetal bone growth. Vitamin D inhibits sexually transmitted infections in mothers and promotes fetal bone growth. Prevention of vitamin D deficiency, supplementation, or outdoor activities is recommended.

The effect of proto-type wearable light-emitting devices on serum 25-hydroxyvitamin D levels in healthy adults: a 4-week randomized controlled trial

BACKGROUND

Many people in modern society have insufficient exposure to ultraviolet B (UVB) sunlight, which may lead to vitamin D deficiency. We aimed to investigate the effect of a proto-type wearable light-emitting diode (LED) device emitting UVB light on serum 25-hydroxyvitamin D levels.

METHODS

A total of 136 healthy adults were randomly assigned to receive either an active device emitting UVB light with a peak wavelength of 285 nm (n = 64) or a sham device emitting visible light (n = 72). All participants wore the device for a total of two minutes, one minute on each forearm, every day for 4 weeks. Serum 25-hydroxyvitamin D levels were assessed at baseline, 2, and 4 weeks of intervention, and 2 weeks after the end of the intervention.

RESULTS

A significant difference was found between the experimental and control groups in changes in serum 25-hydroxyvitamin D levels from baseline after two (0.25 ± 3.10 ng/mL vs. -1.07 ± 2.68 ng/mL, p = 0.009) and 4 weeks of intervention (0.75 ± 3.98 ng/mL vs. -1.75 ± 3.04 ng/mL, p < 0.001). In the experimental group, the dropout rate due to mild, self-limiting adverse skin reactions was 11.8% (9/76). The mean total 25-hydroxyvitamin D production after UVB exposure was estimated at 0.031 ng/mL per 1 cm² of skin area.

CONCLUSIONS

A prototype wearable LED UVB device was effective for improving 25-hydroxyvitamin D status. The development of a safer wearable LED device for phototherapy may provide a novel daily, at-home option for vitamin D supplementation.

The Association between Self-Rated Health Status, Psychosocial Stress, Eating Behaviors, and Food Intake According to the Level of Sunlight Exposure in Korean Adults

Sunlight exposure has been reported to have various beneficial effects on human health. This study investigated the relationship between self-rated health status, psychosocial stress, eating behaviors, and food intake according to sunlight exposure in 948 adults. Sunlight exposure was classified as less than one hour, less than three hours, and greater than three hours. Of the participants, 49.2% had fewer than three hours of daily exposure to sunlight. Regarding participants exposed to sunlight for less than one hour, the largest response was that they did not engage in outdoor activities on weekdays or weekends, and the rate of being outdoors in the shade on sunny days was the highest in this group at 42.7%. Furthermore, the participants exposed to sunlight for less than one hour had a lower health response than the other two groups, and there were significantly more participants classified in the stress risk group. Regarding eating habits, those with less than an hour of exposure to sunlight frequently ate fried foods, fatty foods, added salt, and snacks, and had significantly lower total dietary scores or three regular meals. Additionally, their frequency of consumption of cereals, milk and dairy products, orange juice, and pork was also significantly lower than the other groups. Thus, it is necessary to provide sufficient guidelines for adequate sunlight exposure and food intake because participants with low sunlight exposure may have low vitamin D synthesis and insufficient food intake.

Recent Information on Vitamin D Deficiency in an Adult Korean Population Visiting Local Clinics and Hospitals

We retrospectively reviewed serum 25-hydroxy vitamin D (25(OH)D) test results from an adult Korean population visiting local clinics and hospitals between July 2017 and December 2021 to gather recent information on the prevalence of vitamin D deficiency. The prevalence of vitamin D deficiency status was investigated according to criteria offered by various clinical guidelines. During the study period, 180,289 subjects (29,658 men and 150,631 women) were tested for 25(OH)D. The overall prevalence rates of vitamin D deficiency status based on 25(OH)D level were as follows: 0.4% for <5 ng/mL, 12.5% for <10 ng/mL, 20.6% for <12 ng/mL, 49.4% for <20 ng/mL, and <75.3% for <30 ng/mL. Women tested their 25(OH)D level more frequently than men, and the overall prevalence of 25(OH)D < 10 ng/mL was higher among women than men, while that of 25(OH)D <30 ng/mL was lower among women than men. Among age groups, the prevalence of 25(OH)D <30 ng/mL was higher in younger patients (20s−40s, 79.6−85.5%) than older ones (≥50 years, 62.6−69.2%). The overall prevalence of vitamin D deficiency decreased over time from 2018 to 2021. Future studies are needed to clarify the clinical impact of this change.

Evidence and suggestions for establishing vitamin D intake standards in Koreans for the prevention of chronic diseases

BACKGROUND/OBJECTIVES

Vitamin D is produced in the skin during sun exposure and is also ingested from foods. The role of vitamin D needs to be considered in the prevention and management of various diseases. Moreover, since the majority of Koreans spend their days indoors, becoming susceptible to the risk of vitamin D deficiency. The current study aims to prepare a basis for determining dietary reference intake of vitamin D in Korea, by reviewing the evidence against various diseases and risks.

MATERIALS/METHODS

Literature published in Korea and other countries between 2014 and 2018 was prioritized based on their study design and other criteria, and evaluated using the RoB 2.0 assessment form and United States Department of Agriculture Nutrition Evidence Library Conclusion Statement Evaluation Criteria.

RESULTS

Of the 1,709 studies, 128 studies were included in the final systematic analysis after screening. To set the dietary reference intakes of vitamin D based on the selected articles, blood 25(OH)D levels and indicators of bone health were used collectively. Blood vitamin D levels and ultraviolet (UV) exposure time derived from the Korean National Health and Nutrition Examination Survey were analyzed to establish the dietary reference intakes of vitamin D for each stage of the life cycle. The adequate intake levels of vitamin D, according to age and gender, were determined to be in the range of 5–15 μg/day, and the tolerable upper intake level was established at 25–100 μg/day.

CONCLUSIONS

The most important variable for vitamin D nutrition is lifestyle. A balanced diet comprising foods with high contents of vitamin D is important, as is vitamin D synthesis after UV exposure. The adequate intake level of vitamin D mentioned in the 2015 Dietary Reference Intakes for Korean (KDRI) remained unchanged in the 2020 KDRI for the management of vitamin D nutrition in Koreans.

Vitamin D deficiency and associated factors in south Korean childbearing women: a cross-sectional study

Background

Adequate levels of vitamin D are important for women of childbearing age as vitamin D helps maintain the pregnancy and ensures proper maternal and fetal bone metabolism and fetal skeletal development. However, vitamin D deficiency is a health problem prevalent in women of all ages, worldwide. This study aimed to determine the current status of serum vitamin D levels and the risk factors for vitamin D deficiency among South Korean nurses of childbearing age.

Methods

Serum levels of 25-hydroxyvitamin D (25[OH]D) were measured in 1594 registered nurses aged 20 to 45 years who are participants in an ongoing prospective cohort study of the Korean Nurses’ Health Study initiated in 2013. The participants completed surveys about demographic and occupational characteristics and physical and psychological health. We examined associations with vitamin D deficiency through multivariable logistic regression analysis.

Results

The average blood 25(OH) D concentration of the participants was 12.92 ng/mL (4.0–63.4 ng/mL), while the prevalence of vitamin D deficiency (< 20 ng/mL) was 89% (1419/1594). Multivariable logistic regression showed that significant risk factors for vitamin D deficiency included month of sampling (there was a lower level of vitamin D deficiency in winter than in spring, summer, or fall), age (women in their 20s had a lower vitamin D level than those in their 30s and 40s), and stress symptoms. Vitamin D levels were not associated with body mass index, physical activity, and depressive symptoms.

Conclusions

This study showed a high prevalence of vitamin D deficiency in Korean female nurses. Serum levels of vitamin D were associated with age and season. Vitamin D deficiency should be recognized as one of the primary health concerns among young women. More proactive actions, such as vitamin D supplements and food fortification, are needed to improve vitamin D deficiency in high-risk groups.

The Association between Serum Vitamin D Concentration and Colon Polyp: A Cross-Sectional Study Using Health Care Screening Database in a Tertiary Hospital in Korea

Background

As indoor activity increases with modern lifestyles changes, reduced exposure to sunlight may lead to reduced vitamin D synthesis. Previous studies demonstrated that increased vitamin D level is associated with decreased risk of colon cancer; therefore, this study attempted to determine the association between vitamin D and colon polyps, which may be precancerous lesions, in participants who underwent colonoscopy exams.

Methods

A total of 31,004 participants who underwent routine health checkups, including vitamin D level and colonoscopy, at Samsung Medical Center in South Korea from 2010 to 2018 were included in the study. Colorectal polyps were diagnosed through biopsy after performing colonoscopy exams. Participants were categorized into three groups according to level of vitamin D (deficient: <20 ng/mL), insufficient: 20≤ vitamin D <30 ng/mL, and sufficient: ≥30 ng/mL). We analyzed the presence of colorectal polyps according to vitamin D level, and performed multiple logistic regression analyses for the association between vitamin D level and colorectal polyps.

Results

About 50% of participants had colorectal polyps (hyperplastic polyp, n=4,864; adenomatous polyp, n=10,470; adenocarcinoma, n=24). There were no significant associations between vitamin D categories and colorectal polyp and colorectal cancer. However, when further analyzing by type of polyp, the risk of hyperplastic polyps significantly decreased with increasing vitamin D levels (P for trend=0.006).

Conclusion

We did not find evidence for an association between vitamin D and overall colorectal polyps; however, we observed a trend for decreased odds of hyperplastic polyps with increased vitamin D levels in comparison to vitamin D deficient subjects.

Independent and interactive associations of season, dietary vitamin D, and vitamin D-related genetic variants with serum 25(OH)D in Korean adults aged 40 years or older

Only limited information is available on the inter-relationships between genetic and non-genetic factors such as diet and sunlight exposure with serum 25-hydroxyvitamin D [25(OH)D] concentration. This cross-sectional study aimed to examine the independent and interactive associations of season, dietary vitamin D intake, and SNPs of 11 vitamin D-related candidate genes with serum 25(OH)D concentration among 2,721 adults aged ≥40 years at baseline from the Yangpyeong cohort, a part of the Korean Genome Epidemiology Study (KoGES). The interactions between season or dietary vitamin D and 556 SNPs were evaluated using 2-degree of freedom joint tests. Season was strongly (p_difference = 1.00 × 10^-12) and dietary vitamin D intake was slightly but significantly associated with serum 25(OH)D concentration (p_difference = 0.0119). Among five SNPs (rs11723621-GC, rs7041-GC, rs10500804-CYP2R1, rs7129781-CYP2R1, and rs2852853-DHCR7) identified in the screening steps, only one, rs10500804-CYP2R1, significantly interacted with season (p_interaction = 8.01 × 10^-5). The inverse association between number of minor alleles of rs10500804-CYP2R1 and concentration of 25(OH)D was significant only in summer/fall. Conversely, dietary vitamin D intake was positively associated only in winter/spring. In conclusion, season, dietary vitamin D intake, and four SNPs in GC, CYP2R1, and DHCR7 are independently and rs10500804-CYP2R1 is interactively associated with serum 25(OH)D concentration. Serum 25(OH)D is influenced by genotype of rs10500804-CYP2R1 in summer/fall when sunlight exposure is high, while dietary vitamin D intake is an important determinant of serum 25(OH)D during the seasons with low cutaneous vitamin D synthesis.

Impacts of serum vitamin D levels on sleep and daytime sleepiness according to working conditions

STUDY OBJECTIVES

Low serum vitamin D levels are known to be associated with working conditions and poor sleep, but precedent studies on this issue were limited by the absence of objective sleep measurements or clear distinction between daytime and night shift work. Hence, we aimed to examine serum vitamin D levels and sleep in daytime and night-shift workers using actigraphy.

METHODS

A total of 412 night-shift and 432 daytime workers at Seoul National University Bundang Hospital was recruited. All participants completed questionnaires regarding demographic and clinical characteristics. They underwent blood tests for serum vitamin D levels. Objective sleep data were obtained from 150 night-shift workers and 203 daytime workers using actigraphy.

RESULTS

There was no significant difference in serum vitamin D levels between night-shift and daytime workers after controlling for possible confounders. In daytime workers, vitamin D deficiency was closely related to shorter duration of total sleep time (odds ratio [OR]: 3.07, 95% confidence interval [CI]: 1.51-6.26, P = .002) and higher risk of excessive daytime sleepiness (OR: 2.20, 95% CI: 1.30-3.74, P = .003). Deficient vitamin D was also associated with life quality impairment regarding psychological health (OR: 1.83, 95% CI: 1.07-3.29, P = .028) and social relationship (OR: 1.78, 95% CI: 1.10-2.88, P = .020). However, in night-shift workers, no significant association was observed between serum vitamin D level and sleep parameters, depressive/anxiety symptoms, or quality of life.

CONCLUSIONS

The modest adverse impact of poor vitamin D status on sleep could be attenuated by substantial shift work-related sleep disturbances in night-shift workers. Further studies might be needed to clarify the beneficial effect of vitamin D supplementation for improving sleep and daytime sleepiness in workers with various working conditions.

Associations between Physical Activity, Sunshine Duration and Osteoporosis According to Obesity and Other Lifestyle Factors: A Nested Case-Control Study

(1) Background: The purpose of the study was to evaluate the associations between physical activity (PA), sunshine duration (SD) and the occurrence of osteoporosis according to lifestyle status. (2) Methods: Data from the Korean National Health Insurance Service-National Sample Cohort (NHIS-NSC) collected from 2009 to 2015 were used. Osteoporosis (n = 19,351) and control (n = 38,702) participants were matched in a 1:2 ratio according to age, sex, income, and region of residence. PA was classified as moderate- to high-intensity PA (MHPA) or low-intensity PA (LPA) based on the International Physical Activity Questionnaire (IPAQ). SD was classified as short (≤6 h) or long (>6 h). Conditional logistic regression was used to calculate the odds ratios (ORs) with 95% confidence intervals (CIs) of MHPA and long SD for the occurrence of osteoporosis. Subgroup analyses were performed according to SD (or PA), obesity, smoking, and alcohol consumption. (3) The adjusted OR of MHPA for osteoporosis was 0.90 (95% CI = 0.87-0.94). The results were consistent in the age/sex, SD, obesity, smoking, and alcohol consumption subgroups, but not the <60-year-old male and underweight subgroups. The adjusted OR of long SD for osteoporosis was 0.96 (95% CI = 0.93-1.00). The findings were consistent in the <60-year-old female, obese, nonsmoker, and <1 time a week alcohol consumption subgroups. (4) Conclusions: We suggest that both higher intensity of PA and long SD could decrease the risk of osteoporosis. Specifically, PA could decrease the risk of osteoporosis in individuals with most characteristics except male sex or underweight. Long SD could decrease the risk of osteoporosis in young females, obese individuals, nonsmokers, and individuals with lower alcohol consumption.

Association between shift work and biological factors including FGF-23, klotho, and serum 25-(OH) vitamin D3 among Korean firefighters: a cross-sectional study

STUDY OBJECTIVES

Shift work is known to be detrimental to an individual's health as it disrupts the circadian rhythm and is a risk factor for cancer. It has been reported that elevated fibroblast growth factor (FGF)-23, increased serum soluble α-klotho, and decreased vitamin D3 are associated with cancer progression. We studied the relationship between shift work and the levels of FGF-23, α-klotho, and vitamin D3 amongst firefighters, as they work in long shifts outside the traditional daytime schedule.

METHODS

The study consisted of 450 participants who were firefighters. We measured FGF-23, α-klotho, and vitamin D3 levels in their blood and a set of questionnaires were given to the participants to evaluate their health habits. After determining and adjusting for potential confounding factors, we compared the levels of FGF-23, α-klotho, and serum vitamin D3 by job and shift types.

RESULTS

FGF-23 and α-klotho levels were significantly higher in shift workers than traditional day workers, and in 3-day cycle shift workers than workers with another shift schedule. When the levels of these substances were compared based on different types of jobs, firefighters had a lower level of vitamin D3. We conclude that shift work is positively correlated with the levels of FGF-23 and α-klotho.

CONCLUSIONS

Levels of FGF-23 and α-klotho were linked to shift work and job types. Although vitamin levels did not differ by shift types, vitamin D3 levels were lower in firefighters. These findings suggest that high levels of FGF-23 and α-klotho are potential risk factors for cancer among firefighters.

Vitamin D deficiency and mortality among critically ill surgical patients in an urban Korean hospital

Critically ill patients in intensive care units (ICUs) are exposed to various risk factors for vitamin D deficiency. Vitamin D deficiency in extended-stay patients may result in decreased muscle mass and increased fat tissue, which may impair rehabilitation and recovery. Our study aimed to evaluate the degree of serum vitamin D deficiency in critically ill surgical patients and its association with clinical outcomes. Clinical data from 186 adult male (n = 121; 65.1%) and female (n = 65; 34.9%) patients hospitalized in surgical ICUs at Ajou University Hospital from April 2015 to September 2016 were retrospectively analyzed. All adult surgical patients between the age of 18 and 88 years were enrolled. The mean serum 25-hydroxyvitamin D (25[OH]D) level of all patients was 17.8 ng/mL. A total of 120 patients (64.5%) with serum 25(OH)D levels < 20 ng/mL were classified as the deficiency group. A prolonged hospital stay was observed among the deficiency group but was not statistically significant (p = 0.824). Serum 25(OH)D levels were significantly correlated with age but inversely correlated with Sequential Organ Failure Assessment (SOFA) score, selenium, triglyceride, and C-reactive protein levels. There was no significant difference in mortality rates between the group with a vitamin D injection and the group without a vitamin D injection (14.6% vs. 16.9%, p = 0.074). Vitamin D deficiency was common in surgical ICU patients; however, vitamin D levels were higher in older patients. In conclusion, vitamin D deficiency was inversely associated with the SOFA severity score (Correlation Coefficient -0.165, p = 0.024) but was not associated with the length of hospital or ICU stay and mortality.

Menopause-Associated Lipid Metabolic Disorders and Foods Beneficial for Postmenopausal Women

Menopause is clinically diagnosed as a condition when a woman has not menstruated for one year. During the menopausal transition period, there is an emergence of various lipid metabolic disorders due to hormonal changes, such as decreased levels of estrogens and increased levels of circulating androgens; these may lead to the development of metabolic syndromes including cardiovascular diseases and type 2 diabetes. Dysregulation of lipid metabolism affects the body fat mass, fat-free mass, fatty acid metabolism, and various aspects of energy metabolism, such as basal metabolic ratio, adiposity, and obesity. Moreover, menopause is also associated with alterations in the levels of various lipids circulating in the blood, such as lipoproteins, apolipoproteins, low-density lipoproteins (LDLs), high-density lipoproteins (HDL) and triacylglycerol (TG). Alterations in lipid metabolism and excessive adipose tissue play a key role in the synthesis of excess fatty acids, adipocytokines, proinflammatory cytokines, and reactive oxygen species, which cause lipid peroxidation and result in the development of insulin resistance, abdominal adiposity, and dyslipidemia. This review discusses dietary recommendations and beneficial compounds, such as vitamin D, omega-3 fatty acids, antioxidants, phytochemicals—and their food sources—to aid the management of abnormal lipid metabolism in postmenopausal women.

Obesity and Vitamin D Insufficiency among Adolescent Girls and Young Adult Women from Korea

Although there is evidence of the biological mechanisms by which obesity may induce vitamin D insufficiency or deficiency, limited epidemiological studies have been conducted, especially among Asian adolescent girls and young adult women who are at a high risk of vitamin D deficiency. This study aimed to examine the cross-sectional association between obesity and vitamin D insufficiency among adolescent girls and young adult women in Korea. We used data from the Korea National Health and Nutrition Examination Survey (KNHANES) 2008–2014, and 3623 girls and young adult women aged 12–29 years were included. Demographic and lifestyle data were collected using a self-administered questionnaire from the health interview survey. Serum 25-hydroxyvitamin D (25(OH)D) level, body mass index (BMI), and body fat percentage (BF%) were measured during health examinations. Multivariable logistic regression was used considering the complex, multistage probability sample design of KNHANES. In the multivariable-adjusted analyses, obese girls and women, defined by BMI, were more likely to have a higher prevalence of vitamin D insufficiency (odds ratio [OR]: 1.49, 95% confidence interval [CI]: 1.03–2.17). This association was also evident for BF%. Participants with ≥30% BF% had a significantly higher prevalence of vitamin D insufficiency (OR: 1.52, 95% CI: 1.07–2.16). Obesity may worsen vitamin D insufficiency among adolescents and young women because of the fat-soluble characteristics of vitamin D and related health behaviors, such as a lack of outdoor activity. Further large-scale prospective cohort studies or randomized controlled trials are warranted to confirm this causality.

Vitamin D Deficiency and Neurologic Outcome After Sudden Cardiac Arrest

BACKGROUND

Vitamin D deficiency is related to various cardiovascular diseases, including sudden cardiac arrest (SCA). This study investigated the association of vitamin D level with neurologic outcome and mortality after resuscitation from SCA.

PATIENTS AND METHODS

We enrolled patients who were successfully resuscitated from out-of-hospital cardiac arrest of presumed cardiac cause in Severance Cardiovascular Hospital as a prospective cohort registry. Baseline blood samples including pH, lactate, and vitamin D were obtained without fluid replacement just after hospital admission. Outcome was assessed by cerebral performance category (CPC) score at 1 month after SCA. Favorable outcome was defined as survival with CPC score of 1 or 2, whereas unfavorable one as death or survival with CPC scores of 3 through 5. Severe vitamin D deficiency was defined as 25(OH)D <10 ng/mL.

RESULTS

A total of 163 patients were included. Overall 96 (59%) patients had a favorable neurologic outcome, whereas 67 patients (41%) showed unfavorable outcome, including 37 (23%) mortality. Patients with unfavorable outcome were likely to be female and have initial non-shockable rhythm, longer arrest time, severe shock, diabetes, and baseline renal dysfunction. In multivariate analysis, severe vitamin D deficiency was one of the poor prognostic factors of both unfavorable neurologic outcome and mortality after SCA.

CONCLUSIONS

Vitamin D deficiency is very prevalent and strongly associated with both unfavorable neurologic outcome and mortality in patients resuscitated from SCA.

The Relationship Between Serum 25-Hydroxyvitamin D Levels and Physical Performance in Community-Dwelling Older Adults

Background

Vitamin D deficiency is a risk factor for musculoskeletal health in older adults. While many studies have explored the relationship between vitamin D deficiency and fractures, few have examined the relationship between vitamin D and physical performance. We, therefore, sought to evaluate the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and physical performance in community-dwelling older adults.

Methods

A single-center, cross-sectional study was performed using data collected from 132 individuals aged 60 years or older who were living independently and who participated in the National Health Insurance Service health check-up between May and December 2016. Physical performance was assessed using a short physical performance battery (SPPB). Linear regression was used to examine the association between 25(OH)D levels and physical performance after adjustment for sociodemographic variables, behavioral characteristics, and body mass index.

Results

Approximately 36.5% of male and 50.7% of females had vitamin D levels indicative of deficiency (serum 25(OH)D <20.0 ng/mL). 25(OH)D levels were significantly associated with the chair stand SPPB scores in male and females but not with those of the walking and balance tests. After adjustment for potential confounders, there remained a linear association between 25(OH)D levels and the chair stand test for both sexes.

Conclusion

Lower serum 25(OH)D levels were associated with poor physical performance (chair stand score) among community-dwelling older adults in Korea. Further prospective studies are needed to verify these results.

Genetic influence on serum 25-hydroxyvitamin D concentration in Korean men: a cross-sectional study

Background

Hypovitaminosis D is prevalent worldwide. It is more prevalent in Eastern Asia region, including Korea. In addition to various environmental factors that influence serum 25-hydroxyvitamin D (25(OH)D) concentration, genetic influence also plays a significant role based on studies estimating the heritability of 25(OH)D in non-Asian populations. The objective of this study was to determine the genetic influence on serum 25(OH)D concentration in Korean men using the twin and family data.

Methods

A total of 1126 Korean male adult twins and family members from the Healthy Twin Study with serum 25(OH)D measurement were included in this cross-sectional study. Intraclass correlation coefficients (ICCs) and heritability were calculated by mixed linear regression analysis and quantitative genetic analysis after adjusting for environmental and lifestyle factors.

Results

Mean (± standard deviation; SD) of serum 25(OH)D concentration was 15.34 ± 6.18 ng/ml. The prevalence of vitamin D insufficiency was 19.8% and that of vitamin D deficiency was 77.9%. After adjusting for age, the highest ICC (0.61) was observed for monozygotic twin pairs while the lowest ICC (0.31) was found for father-son pairs. Age-adjusted heritability was estimated to be 58%. When physical activity, multivitamin intake and season of blood sampling were further considered, the ICC and heritability did not materially change. In the sensitivity analysis after excluding known multivitamin users, age-adjusted heritability was reduced to 44%.

Conclusions

In our study of Korean male twins and family members, heritability of 25(OH)D was moderately high. This supports the finding that genetic factors have significant influence on vitamin D status.

Electronic supplementary material

The online version of this article (10.1186/s12263-018-0621-7) contains supplementary material, which is available to authorized users.

Laboratory confirmation of the effect of occupational sun exposure on serum 25-hydroxyvitamin D concentration

Vitamin D concentration is known to correlate with various parameters. A major source of vitamin D is synthesis in the skin; thus, the duration of sun exposure is known to correlate with serum vitamin D levels. We compared serum levels of vitamin D between 2 occupational groups in Korea: the fisherman group, the most sun-exposed, and the general occupation group, relatively less sun-exposed. This study was conducted on 140 healthy fishermen and 140 healthy residents with various occupations, all of whom resided in the southernmost region of Korea, from June to August 2016. We compared serum concentrations of 25-hydroxyvitamin D (25(OH)D) in both occupation groups by gender and age and suggested vitamin D reference interval for the region. Mean serum 25(OH)D concentrations in the general occupation and fisherman group were 13.60 ± 6.43 and 23.74 ± 8.88 ng/mL, respectively. Mean serum concentration of 25(OH)D was 1.7 times higher in the fisherman group compared with the general occupation group, which was statistically significant (P < .001). Approximately 98% of subjects in the general occupation group and 78% of subjects in the fisherman group demonstrated either vitamin D insufficiency or deficiency. Calculated serum 25(OH)D reference interval for all subjects in our study was 3.8 to 44.4 ng/mL. Despite exposure to a large amount of sunlight, 78% of subjects in the fisherman group presented with either vitamin D deficiency or insufficiency. By taking laboratory measurements of serum 25(OH)D concentrations in fisherman, who were expected to have the highest vitamin D concentrations in Korea, this study could be epidemiologically useful.

Association Between Vitamin D Insufficiency and Metabolic Syndrome in Patients With Psychotic Disorders

OBJECTIVE

This study examined the association between vitamin D and metabolic syndrome in patients with psychotic disorders.

METHODS

The study enrolled 302 community-dwelling patients with psychotic disorders. Sociodemographic and clinical characteristics, including blood pressure, physical activity, and dietary habit were gathered. Laboratory examinations included vitamin D, lipid profile, fasting plasma glucose, HbA1c, liver function, and renal function. Vitamin D insufficiency was defined as <20 ng/mL. Clinical characteristics associated with vitamin D insufficiency were identified.

RESULTS

Among the 302 participants, 236 patients (78.1%) had a vitamin D insufficiency and 97 (32.1%) had metabolic syndrome. Vitamin D insufficiency was significantly associated with the presence of metabolic syndrome (p=0.006) and hypertension (p=0.017). Significant increases in triglycerides and alanine transaminase were observed in the group with a vitamin D insufficiency (p=0.002 and 0.011, respectively). After adjusting for physical activity and dietary habit scores, vitamin D insufficiency remained significantly associated with metabolic syndrome and hypertension.

CONCLUSION

Vitamin D insufficiency was associated with metabolic syndrome and was particularly associated with high blood pressure, although the nature, direction and implications of this association are unclear.

Relationship between Serum Vitamin D Status and Metabolic Risk Factors among Korean Adults with Prediabetes

Serum vitamin D status has been associated with prediabetes and metabolic syndrome. Evidence for the increased risk of metabolic disorders in individuals with prediabetes and a low vitamin D status is limited and uncertain. Furthermore, it has not been confirmed whether this possible relationship occurs in the Korean population. The aim of this study was to assess serum vitamin D status and to examine the relationship between serum vitamin D levels and metabolic risk factors in Korean adults with prediabetes. This cross-sectional study was conducted among 60 subjects aged 20-65 years. Participants had fasting glucose levels of 100 to 125 mg/dl. A questionnaire was used to assess vitamin D synthesis from sun exposure and a dietary intake examined using 3-days dietary records. Clinical and biochemical data were also collected. The 2009 harmonized definition of metabolic syndrome was used. Serum vitamin D levels were classified according to criteria from the 2011 Institute of Medicine report. The majority of subjects (75%) had a serum 25(OH)D level < 20 ng/ml, and among them, 31.1% were vitamin D deficiency (< 12 ng/ml). The proportion (42.9%) of subjects having low HDL-cholesterol was the highest among vitamin D deficiency (< 12 ng/ml) group (12 to < 20 ng/ml: 16.1%, ≥ 20 ng/ml: 6.7%). We observed an inverse relationship between 25(OH)D levels and TG, AI (β = -6.355, SE = 2.463; β = -0.020, SE = 0.008) after adjusted confounders. Korean adults with prediabetes were more likely to have low serum 25(OH)D levels. A sufficient 25(OH)D level may have possible beneficial effects on lipid profiles.