Elsevier

Nutrition

Volume 31, Issues 7–8, July–August 2015, Pages 975-980
Nutrition

Applied nutritional investigation
Associations of serum β-carotene and retinol concentrations with insulin resistance: The Toon Health Study

https://doi.org/10.1016/j.nut.2015.02.015Get rights and content

Highlights

  • This study found that higher serum β-carotene was associated with higher intake of green and yellow vegetables, and also was associated with lower risk for insulin resistance.

  • This study suggested that higher serum β-carotene have a potential protective effect against insulin resistance.

  • We conducted oral glucose tolerance tests and assessed insulin resistance using by 1- and 2-h postloaded serum insulin and glucose levels.

Abstract

Objective

Although green and yellow vegetables have beneficial effects against type 2 diabetes, the relationship of their nutritive content with insulin resistance is poorly understood. The aim of this study was to examine the associations of serum β-carotene and retinol concentrations with glucose and insulin concentrations.

Methods

We recruited 951 Japanese men and women ages 30 to 79 y who were not undergoing treatment for diabetes and measured their serum β-carotene and retinol concentrations. A 75-g oral glucose tolerance test was performed and the homeostasis model assessment for insulin resistance (HOMA-IR) and the Matsuda Index were calculated as measures of insulin resistance. Several confounding factors were adjusted for with multivariable logistic models.

Results

Multivariable-adjusted odds ratios of the highest quartile of serum β-carotene compared with the lowest quartile for HOMA-IR >1.6 and Matsuda Index <4.9 were 0.56 (95% confidence interval, 0.34–0.94) and 0.62 (0.37–1.02), respectively. When stratified by sex and overweight status, these associations were observed for women and non-overweight individuals. Serum retinol concentration was not associated with either index. Furthermore, according to the nutritional survey, serum β-carotene concentration was associated with green and yellow vegetable intake (P = 0.01).

Conclusion

Our findings suggest that higher serum β-carotene levels, associated with higher intake of green and yellow vegetables, confer beneficial effects against insulin resistance.

Introduction

Type 2 diabetes is a major lifestyle-related disease with an increasing global prevalence. The World Health Organization reported that the prevalence of type 2 diabetes was 6.4% in 2010 and it is expected to rise to 7.7% by 2030 [1]. One meta-analysis of six cohort studies showed that an increase in daily food intake of 1.15 servings of green leafy vegetables was associated with a 14% reduction in the incidence of type 2 diabetes [2]. Accordingly, lower vegetable intake appears to be linked to a higher prevalence of type 2 diabetes in the Japanese population as well.

Vitamin A is a part of a group of fat-soluble and antioxidant vitamins, whose members include retinol and carotenoids; the antioxidant and anti-inflammatory capacities of the latter, in particular, may protect against the development of type 2 diabetes [3], [4]. Although humans can fractionally convert carotenoids to retinol [5], they are not able to naturally synthesize carotenoids; therefore, dietary intake from fishes and meats is important for obtaining retinol, whereas vegetable intake is important for obtaining carotenoids [6].

Serum carotenoid concentrations were inversely associated with fasting glucose, insulin [7], and homeostasis model assessment for insulin resistance (HOMA-IR) levels in US adults [8]. Furthermore, serum β-carotene and lycopene concentrations were lower in individuals with glucose abnormalities or diabetes than in those without these conditions [7], [9]. Although a similar association was found in Japanese men and women [10], the volume of evidence for Asian populations remains very limited.

Additionally, few previous studies have assessed insulin resistance (IR) and the prevalence of diabetes using an oral glucose tolerance test (OGTT), which is a gold-standard method for the clinical assessment of glucose tolerance. For Asian individuals, it is important to evaluate glucose tolerance based on a 2-h postprandial glucose level in the OGTT because diagnosis based on fasting glucose concentrations alone often fails to detect impaired glucose tolerance [11].

The aim of this study was to examine the associations of serum β-carotene and retinol concentrations with glucose and insulin levels in accordance with the OGTT protocols in a general population of Japanese adults.

Section snippets

Participants

We conducted a cross-sectional study as part of the Toon Health Study initiated in 2009, which was a prospective cohort study of the Japanese general population. The cohort study was intended to characterize environmental risk factors related to incident diabetes and cardiovascular disease. Participants (ages 30–79 y) were recruited from the general population who were living in Toon City, Ehime Prefecture, Japan [12], [13], [14].

Of the 1,109 participants enrolled from 2009 to 2010, we excluded

Results

Age- and sex-adjusted means and percentages of investigated markers according to quartiles of serum β-carotene and retinol concentrations are shown in Table 1. Serum β-carotene concentration was inversely associated with male sex and current smoking status. It was also inversely associated with mean BMI in addition to fasting, 1- and 2-h postprandial serum insulin and glucose levels. It was also inversely associated with HOMA-IR, and HbA1c. There were positive associations with mean age and the

Discussion

The present study showed that serum β-carotene concentration was inversely associated with IR in middle-aged Japanese individuals, whereas serum retinol concentrations were not. Of note, these associations were more apparent in women and non-overweight adults. We also observed a positive association between serum β-carotene concentration and green and yellow vegetable intake, which suggests that serum β-carotene concentrations are largely dependent on green and yellow vegetable intake.

Our

Acknowledgments

The authors acknowledge the staff members and participants of the Toon Health Study for their valuable contributions to the surveys.

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  • Cited by (0)

    This study was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grants-in-Aid for Research B, No. 22390134 in 2010–2012 and No. 25293142 from 2013, Grant-in-Aid for research C, No. 20590647 in 2008–2010 and No. 20590634 in 2008–2010, No. 23590796 in 2011–2013, Grand-in-Aid for Young Scientists B, No. 25860443 and No. 25860441 from 2013), Health and Labor Sciences Research Grants from the Ministry of Health, Welfare and Labor, Japan (Comprehensive Research on Life-Style Related Diseases including Cardiovascular Diseases and Diabetes Mellitus, No. 201021038 A in 2010–2012). TT, IS, HO, and WN designed the study. KH, KM, EE, HM, ST, and SS collected the data. TK measured serum β-carotene and retinol concentrations. HO and WN reviewed and edited the manuscript, contributing the valuable clinical suggestions. KY wrote the manuscript, and IS had primary responsibility for the final content of the manuscript. All authors contributed to the interpretation of the results and revising of the manuscript. There are no conflicts of interest to declare.

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