Mixed carotenoid supplementation and dysmetabolic obesity: gaps in knowledge

Abstract

Dysmetabolic obesity during childhood and adolescence currently represents one of the greatest therapeutic challenge for healthcare systems worldwide. The global rates of obesity have more than doubled in the last 30 years. Recent meta-analysis from national surveys and food composition studies suggest an inverse association between lower carotenoid levels and the prevalence of Metabolic Syndrome in the general population, independent of serum retinol (vitamin A) levels. In children, two double-blind randomised placebo-controlled studies describing the effects of diet vs. mixed carotenoid supplementation on insulin resistance, adipokines and the rate of accrual of subcutaneous abdominal fat, implicate supplementation of these compounds to achieve targetable levels may be useful in the management of obesity accrual in this population. We will discuss the role of carotenoids and their conversion products (retinoids) in adipogenesis, lipolysis, insulin resistance and the pathophysiology of the metabolic syndrome and review the animal studies, which help support these findings.

Keywords:

• Obesity
• carotenoids
• metabolic syndrome
• visceral fat

Introduction

Dysmetabolic obesity during childhood and adolescence currently represents one of the greatest therapeutic challenge for healthcare systems worldwide. The global rates of obesity have more than doubled in the last 30 years increasing the risk of co-morbidities such as the metabolic syndrome (MetS), type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD) among others. The increased consumption of fruits and vegetables (F/V) among children has been identified by the U.S. Department of Health and Human Services Healthy People 2020 as one of the most important objectives, which could potentially reduce the risk of chronic disease and improve long-term health outcomes worldwide (Matson-Koffman et al. 2005). Despite these concerted efforts and other public health recommendations, few children meet the daily-recommended intake of F/V due to a variety of reasons (Nebeling et al. 2007; Di Noia and Byrd-Bredbenner 2014; Hodder et al. 2018). Adipose tissue is a key organ in the development of dysmetabolic obesity and is considered the main storage site for triglycerides (TG) and other fat soluble micronutrients such as carotenoids (Kaplan et al. 1990). Overweight (OW) children consume more fried food and less total (F/V) leading to a 10–20% lower concentration of serum carotenoids than their normal counterparts (Decsi et al. 1997; Ford et al. 2002; Molnar et al. 2004). Among OW 6–11 year olds the average intake of F/V was 0.94 ± 0.05 cup servings of total fruits, 0.41 ± 0.04 cup servings of fruit juice and 1.08 ± 0.04 cup servings of total vegetables, which falls short of the current recommendations from healthy people 2020 (Nielsen et al. 2014). In this context, supplementation of these essential micronutrients as an adjuvant to macronutrient nutritional counselling therapy may be of importance.

Carotenoids

Carotenoids are C₄₀ lipophilic pigments usually red, orange or yellow in colour which are produced by photosynthetic organisms and are a main source of vitamin A (retinol) in humans. They are used extensively as natural colourants for food, feed, and cosmetics. They are known to be essential for growth and differentiation of adipose cells, regulation of fuel metabolism and constitute an important component of the endocrine effect of adipose tissue on systemic carbohydrate and lipid homeostasis. Carotenoids primary dietary sources are F/V’s, though they can also be obtained from bread, eggs, beverages, fats, and oils (Rao and Rao 2007). In the human diet, there over 40 carotenoids, but only six are ubiquitous in human serum, namely the provitamin A (retinol) carotenoids such as β-carotene, α-carotene, β-cryptoxanthin, and the oxygenated xanthophyll’s such as lycopene, lutein, and zeaxanthin (Rao and Rao 2007). Additionally, epidemiologic studies associate a carotenoid-rich diet (usually resulting from high consumption of F/V) with health benefits (Reunanen et al. 1998; Montonen et al. 2004; Carter et al. 2010). Carotenoids undergo significant degradation and/or metabolism in the human body, it is far from certain whether the native compounds or rather their retinoid metabolites are responsible for the attributed health effects. While typical dietary intakes of carotenoids via whole F/V appear to exert beneficial health effects, supplemental intake with doses above 20 mg/d of purified or synthetic β-carotene may result in adverse effects, including increased cancer risk and total mortality in smokers (Bjelakovic et al. 2012). Many studies in children and adults report an inverse correlation between body mass index (BMI) and β-carotene even after correcting for cholesterol and TG levels (Moor de Burgos et al. 1992; Decsi et al. 1997; Andersen et al. 2006; Canas et al. 2012). Possible explanations are variable intestinal absorption of β-carotene, variable conversion of β-carotene to retinal and all-trans retinoic acid (atRA)via centric cleavage by the BCO1 enzyme, or accelerated clearance of retinol and β-carotene by eccentric metabolism via the BCO2 enzyme (Tourniaire et al. 2009). The implications for this inter-individual variation are important regarding determination of recommended dietary intake (RDI) for dietary carotenoids, especially in vegetarians and obese individuals.

Carotenoids, adiposity and cardio-metabolic disease

Adiposity is determined by a dynamic equilibrium between macronutrient intake and energy expenditure and disruption of this balance leads to obesity and its multiple co-morbidities. Obese individuals with increased risks for T2DM, CVD and all-cause mortality are currently classified as having the MetS both in adults (Haffner et al. 1992; Trevisan et al. 1998; Wilson et al. 1999; Isomaa et al. 2001; Lakka et al. 2002; Hu et al. 2004) and children (Engeland et al. 2004; Biro and Wien 2010). The clustering of at least 3 of 5 cardiometabolic risk components including abdominal adiposity, elevated systolic/diastolic blood pressure, hyperglycaemia and elevated fasting TG or low high-density lipoprotein-cholesterol (HDL-C) make up the definition of MetS, based on the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) criteria (Meigs 2002; Grundy et al. 2005). In children over the age of 10 years, the International Diabetes Federation has set similar cut points as in adults, except for measurement of abdominal adiposity which is specific for age, sex and ethnicity (Alberti 2007). The rising prevalence of obesity and MetS among adults (Beydoun et al. 2011) and children (Ogden et al. 2010) in the US constitutes a major public health threat, leading to higher levels of mortality, disability as well as health care costs (Wang and Beydoun 2007). The prevalence of MetS in the US (National Health and Nutrition Examination Survey NHANES 2001–2006) is reported at 32.0% among men, 29.5% among women, 6.9% among boys and 3.9% among girls. There is an inverse relationship between total carotenoids and MetS, even after controlling for total cholesterol and TG among other potential confounders (Beydoun et al. 2011; Beydoun et al. 2012; Liu et al. 2014; Beydoun et al. 2019). Total carotenoids are inversely related to BMI, homeostasis model assessment-insulin resistance (HOMA-IR) and c-reactive protein (hs-CRP) suggesting targeted carotenoid supplementation may provide significant benefit due to their anti-inflammatory and insulin sensitising properties via their interaction in adipose tissue (Beydoun 2012).

Epidemiological studies reporting effects of long term β-carotene supplementation in adults

Approximately 5220 adults participated in the SUpplementation en VItamines et Minéraux AntioXydants (SU.VI.MAX) primary prevention trial and were randomly assigned to receive a supplement containing a combination of antioxidants (AOX) (120 mg of vitamin C, 30 mg of vitamin E, 6 mg of β-carotene, 20 mg of zinc, and 100 μg of selenium) at nutritional doses or a placebo (Czernichow et al. 2009). Baseline serum AOX concentrations of β-carotene and vitamin C, were negatively associated with the risk of MetS; the adjusted odds ratios (and 95% CIs) for the highest compared with the lowest tertile were 0.34 (0.21, 0.53; p for trend =.0002) and 0.53 (0.35, 0.80; p for trend =.01), respectively. A high concentration of zinc, in the upper part of the normal range, was associated with an increased risk of MetS. AOX supplementation for 7.5 years did not affect the risk of MetS (Czernichow et al. 2009) however the authors suggest that it is possible that the positive effect of β-carotene and vitamin C on the risk of MetS was counterbalanced by the negative effect of zinc supplementation. In addition the baseline levels of β-carotene differed between men (0.46 ± 0.30 µmol/L) and women (0.75 ± 0.67 µmol/L) and may have been relatively high enough to indicate that the participants in this study may have had healthier diets and lifestyles than the population at large (Czernichow et al. 2009).

The Physicians Health Study randomised a total of 22,071 healthy US male physicians aged 40 to 84 years in a double-blind, placebo-controlled trial, from 1982 to 1995 to 50 mg of β-carotene every other day for 12 years and more than 99% of the participants had complete follow-up. During the follow-up period, 396 incident cases of T2DM in the β-carotene and 402 cases in the placebo group were reported, for a RR of 0.98 (95% CI, 0.85–1.12). When the period of risk was subdivided by years of follow-up, no benefit was observed for any time period or duration of treatment (Liu et al. 1999).

Similar results were reported in the α-tocopherol, β-carotene Cancer Prevention (ATBC) Study, a double-blind, controlled trial, 29,133 male smokers aged 50–69 years were randomised to receive either α-tocopherol (50 mg/day) or β-carotene (20 mg/day) or both agents or placebo daily for 5–8 years (median 6.1 years). Neither supplementation significantly affected the incidence of diabetes: the RR was 0.92 (95% CI 0.79–1.07) for participants receiving α-tocopherol compared with non-recipients and 0.99 (95% CI 0.85–1.15) for participants receiving β-carotene compared with non-recipients (Kataja-Tuomola et al. 2008). In the Physicians Health Study β-carotene concentrations went from 0.56 to 2.24 µmol/L (Satterfield et al. 1990) and in the ATBC study the concentrations went from 0.34 to 5.60 µmol/L which are significantly higher than those achieved by diet alone (Liu et al. 1999; Kataja-Tuomola et al. 2008).

In the largest European prospective case-cohort study published to date (EPIC Inter Act consortium accross 26 study centers) investigators ascertained and verified 12 403 individuals with incident T2DM over 3.99 million person years of follow-up from a cohort of 340 234 participants with stored blood and buffy coats and they suggest that a coposite biomarker score comprising of vitamin C and individual carotenoids vs. total carotenoids inversely associated with T2DM incidence with a hazard ratio of 0.77, 0.66, 0.59, and 0.50 for quintile groups 2–5 compared with group 1 (the lowest group). They also report the median self reported F/V intake in grams /day was 274 g/day, 396 g/day, and 508 g/day for participants in categories defined by groups 1, 3, and 5 of the composite biomarker score, respectively. One standard deviation difference in the composite biomarker score, equivalent to a 66 (95 % CI, 61 to 71) g/day difference in total F/V intake, was associated with a hazard ratio of 0.75 (0.67 to 0.83) (Zheng et al. 2020).

Human studies reporting the use of short-term mixed carotenoids in adults and children

Randomised controlled trials (RCT) in adults who increased the intake of F/V from 2 servings to 7 servings per day report doubling (from 0.34 to 0.52 µmol/L) of the β-carotene concentrations by 2 weeks of intervention with stabilisation of the levels for the remainder 8 weeks (Zino et al. 1997). These studies have assessed the potential relationships of increased F/V consumption with the plasma β-carotene concentrations and mRNA expression values of proinflammatory markers associated with MetS in healthy lean young adults (50 men/70 women; 20.8 ± 2.6 years; 22.3 ± 2.8 kg/m²). The highest tertile of energy-adjusted F/V consumption (>660 g/d) was associated with lower plasma concentrations of hs-CRP and homocysteine and with lower soluble ICAM-1, Interleukin-1 Receptor- 1, Interleukin-6, TNFalpha and nuclear factor kappaB1 (NFkappaB1) gene expression in peripheral blood mononuclear cells (PBMC) (p for trend <.05), independently of gender, age, energy intake, physical activity, smoking, BMI, systolic blood pressure and circulating non-esterified fatty acids (Hermsdorff et al. 2010).

Another recent RCT study from The University of Florida tested the effects of giving a mixture of AOX on measures of insulin sensitivity homeostasis model assessment (HOMA-IR) and quantitative insulin sensitivity check index (QUICKY), ICAM-1, endothelial-leukocyte adhesion molecule–1, adiponectin and oxidative stress (lipid hydroperoxides) in overweight and normal-weight individuals (N = 48, 18–30 years). Participants received either AOX (vitamin E, 800 IU; vitamin C, 500 mg; β-carotene, 10 mg) or placebo for 8 weeks. The HOMA-IR values were initially higher in the overweight subjects and were lowered with AOX by week 8 (15% reduction, p =.02). Adiponectin increased in both AOX groups. Soluble ICAM–1 and endothelial-leukocyte adhesion molecule–1 decreased in overweight AOX-treated groups by 6% and 13%, respectively (p < .05). Plasma lipid hydroperoxides were reduced by 0.31 and 0.70 nmol/mL in the normal-weight and overweight AOX-treated groups, respectively, by week 8 (p < .05). The authors concluded that AOX supplementation moderately lowers HOMA-IR and endothelial adhesion molecule levels in overweight young adults. Unfortunately the authors did not report on baseline or changes in serum concentrations of the AOX supplements (Vincent et al. 2009).

In a recent study involving a total of 30 prepubertal boys (age range, 6–10 years), 9 lean boys with BMI ≤85% and 21 overweight (OW) BMI of >85% (Canas et al. 2012; Canas et al. 2015), the effects of short term MCS were reported. All participants received nutrition counselling and were randomised to receive the FVJC or placebo capsules for 6 months. Two active capsules of FVJC provide approximately 3.75 mg of β-carotene, 117 mg of vitamin C, 22.5 IU of vitamin E, 210 mg of folate, 30 mg of calcium, and 21 kJ per day. All subjects underwent a modified rapid intravenous glucose tolerance test at baseline and at the end of the study using 0.5 g/kg glucose (25% dextrose, maximum 25 g) infused over three minutes, and blood was obtained at baseline and three and five minutes after glucose administration. A dual-energy x-ray absorptiometry scan was performed to measure body composition (Hologic Discovery A 45903; Hologic Inc, Bedford, Massachusetts). Dietary composition and micronutrient intake were assessed using a modified 122-item, validated food frequency questionnaire administered by the dietician. Estimates of nutritional intake were quantified with the use of the nutrition analysis program Food Processor (version 9.3.0) developed by ESHA Research (Salem, Oregon). Physical activity was quantified based on the previous week’s activity levels at school or home or during leisure time. Lipid corrected β-carotene (LCβC) was lower (p =.04) and serum retinol (SR) was higher (p =.019) in the OW children compared with the lean children. Retinol binding protein (RBP4) trended to be lower in lean vs. OW children (p = .084), whereas the ratio of RBP4 to SR was not different between these groups. There was a highly significant overall treatment effect between FVJC and placebo in the percent change in β-carotene (p = .001) for the entire cohort but not for the percent change in SR, RBP4, or RBP4/SR ratio. After adjusting for percent weight change, FVJC significantly improved the acute insulin response (AIR) and the calculated glucose disposition index (GDI) by 0.5% vs. placebo − 9% (p = 0.014) and reduced HOMA-IR (p = .014) and enhanced QUICKI (p = .016) in the OW group compared with placebo group suggesting improved insulin sensitivity. Treatment effect by univariate ANOVA on the percent change in abdomina fat mass (AFM) (in kg) for the entire cohort at 6 months showed that the placebo group had a 11.2% increase (95% CI, 4.16 to 18.23) as opposed to a −1.47% (95% CI, 8.31 to 5.37) decrease in the FVJC supplement group (p = .029). Both fatty acid binding protein 4 and 5 (FABP4, FABP5) were higher (p < .01) in the OW v. lean boys and correlated directly with HOMA-IR, AFM, hs-CRP, IL-6, and LCβC (p < .05 for all). FABP4 was associated with adiponectin and AIR (p < .05). FVJC reduced FABP4, HOMA-IR and AFM (p < .05 for all) but not FABP5. The beneficial improvements in FABP4, insulin resistance, glycerides (TG) levels, abdominal fat, suggest that mixed carotenoids, along with other polyphenols, may play a role in the regulation of abdominal adiposity, similar to that reported in animal models and warrant further exploration.

The second study involved 21 obese children who were also randomised to a double-blind placebo-controlled study of a 2-week intense lifestyle intervention program followed by 6 months of mixed carotenoid supplementation (Jarrow Formulas CaroteneAll^®) (Canas et al. 2014, 2017). Results showed β-carotene inversely related to BMI-z; VAT and SAT (p < 0.05 for all). Supplementation resulted in 95 ± 66% increase in β-carotene at 6 months as compared to 3 ± 19% decrease in the placebo group (p = .001). HMW-ADI increased by 43% ± 88% (p < .03) with the supplement and decreased by 5.6 ± 37% (p = NS) in the placebo group. Palmitoleate was lowered by 16 ± 36% at 6 months (p = .03) in the supplement group. There were no significant changes in TG or HOMA-IR. There was a 4% decrease in mean SAT by MRI and an 8% decrease in mean estimated VAT by DEXA (p < .05 for all) in the supplement group.

The authors speculate that there are several mechanisms at play to explain the anti-obesity effects of carotenoids in adipose tissue, which have been subject to recent reviews (Bonet et al. 2015; Coronel et al. 2019; Mounien et al. 2019). The FVJC supplementation, significantly lowered TG (p = .032) in the OW boys and this may have played an important role in improving insulin sensitivity. They also speculate that an increase in atRA by raising β-carotene would lead to down regulation of intestinal lipid absorption by reducing the expression of the SR-BI. All-trans RA via retinoic acid receptors (RAR) induces the expression of the intestinal transcription factor ISX. ISX in turn repressed the expression of SR-B1 and BCO1 thus preventing accumulation of excess β-carotene (Lobo et al. 2010). Although atRA levels were not measured in these studies, a previous intervention study using carrot juice, which is rich in β-carotene, has reported a doubling of plasma atRA acid levels without significant increases in retinol (Ruhl et al. 2008).

Conclusion

Although the mechanisms remain unclear, the augmentation of carotenoids with whole F/V, dried encapsulated juice concentrates or physiological doses of purified mixed carotenoids, may exert a potential direct effect on adipocyte biology, modulating fatty acid metabolism and insulin resistance. The current data also suggests that dietary interventions designed to improve the intake of fruit and vegetables in adults and children call for carefully monitored trials with reliable serum markers of consumption and sophisticated adipose tissue analyses to uncover mechanistic effects. Measurements of specific carotenoids and their conversion products, serum adipokines such as leptin, FABP4 and adiponectin along with energy expenditure by indirect calorimetry or thermogenesis are necessary to unravel the mechanisms linked to fatty acid oxidation in the adipocyte. Research recommendations for full-scale intervention trials to test the preventive potential of mixed carotenoids for chronic diseases will require careful dosing protocols to maintain adequate levels of these important molecules. At the present, there is no resolution of the possible impact of supplementing these nutrients in healthy vs. obese individuals or as preventive measures for chronic disease.

Disclosure statement

The author declares no conflict of interest.