Introduction

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive fat accumulation in the liver with the absence of alcohol and other liver diseases. It is well established that adiposity is a major contributor to NAFLD. Data from epidemiological studies revealed that NAFLD occurrence in up to 70% of overweight adults worldwide [1] and in 90% of morbidly obese adults globally [2]. Nonetheless, a remarkable proportion of individuals having NAFLD with a relatively normal body mass index (BMI), a condition termed as ‘‘non-obese” NAFLD. The prevalence of NAFLD was around 10% in nonobese adults in Western countries, and about 8–19% of Asians with BMI less than 25 kg/ m2 are also found to have NAFLD [3]. Given this trend, a reliable predictor of NAFLD in nonobese people is essential for its prevention and management.

As we best known, the larger the BMI, the higher the metabolic risk. However, individuals within the same BMI status could have considerable differences in the amount and distribution of regional fat depots, leading to variable metabolic risks [4, 5]. Numerous researches highlight the metabolic risk conferred by specific patterns of fat distribution, particularly upper body adiposity [6]. Notably, several studies have recently shown that upper-body subcutaneous adipose tissue, estimated by neck circumference, is a unique fat depot that confer additional metabolic risks beyond generalized and abdominal adiposity [7, 8]. It is reported that neck circumference levels are significantly associated with hyperlipidemia, impaired glucose homeostasis, and insulin resistance, especially in women [7]. All of these supported the investigation of a possible association of neck circumference with NAFLD.

Due, in part, to a transfer from subcutaneous to abdominal visceral fat, women after menopause are prone to metabolic changes [9]. Such metabolic alterations are associated with increased NAFLD risk among normal BMI populations. However, studies that assess neck fat accumulation, as a proxy for upper-body subcutaneous fat, and its relationship with NAFLD among postmenopausal women with normal BMI are still lacking. In the current study, we evaluated the relationship between neck circumference and NAFLD among postmenopausal women with normal BMI.

Participants and methods

Study subjects

Participants were recruited from the China Cardiometabolic Disease and Cancer Cohort (4C) Study, a nationwide prospective cohort study investigating the associations of metabolic factors with specific clinical outcomes, including diabetes, cardiovascular disease, cancer, and all-cause mortality [10, 11]. The data presented in this study are based on the subsamples from the Chongming District in Shanghai, China. From May to November 2011, a total of 2765 postmenopausal women with normal BMI of Chinese origins were enrolled in the study. From June to December 2014, the subjects were invited for follow-up assessments. The cross-sectional survey included 2492 subjects, and the follow-up investigation included 1354 individuals without NAFLD at baseline (Fig. 1). Subjects with the following conditions were excluded from this study: virus hepatitis, autoimmune hepatitis, drug-induced liver disease, current drinkers, ex-drinkers, presence of tumor, biliary obstructive diseases, thyroid dysfunction, total parenteral nutrition, Wilson’s disease, severe renal insufficiency, significant hematologic disorders, and current treatment with systemic corticosteroids.

Fig. 1
figure 1

Overview of the study design

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The study protocol was approved by the Ethics Committee of ** countries. Third, given the diagnosis of NAFLD was based on ultrasound imaging, NAFLD patients in our study were in at least a moderate stage of the disease. Therefore, in the present study, we were unable to determine the relationship between neck circumference and mild-stage NAFLD. Fourth, we did not assess the impact of excluded data on the relationship between neck circumference and incident NAFLD.

Conclusions

Large neck circumference was significantly associated with an increased risk of NAFLD among postmenopausal women with normal BMI. Measurement of neck circumference may provide a more complete understanding of NAFLD risk associated with variation in fat distribution among postmenopausal women with normal BMI.