Basic nutritional investigationAldehydes identified in commercially available ω-3 supplements via 1 H NMR spectroscopy
Introduction
Cardiovascular disease (CVD) is the leading cause of mortality globally [1]. CVD is demonstrably causally related to chronic inflammation [2], [3], [4], among other factors. Studies have suggested that ω-3 fatty acids (FAs) have anti-inflammatory and therefore cardioprotective effects [5], [6], [7], [8], [9]. The long-chain polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the main ω-3 FAs that have been attributed to cardioprotective effects [8]. Because the Western diet is usually low in ω-3 FAs, supplementation is generally recommended [10], [11]. Worldwide, ω-3 FAs are one of the most commonly consumed supplements [12].
Despite the popularity of supplementation with ω-3 oils, benefits for cardiovascular health are unclear [5], [10], [12], [13]. Supplementation with ω-3 may not actually be associated with a lower risk for mortality ascribable to cardiac death, sudden death, myocardial infarction, or stroke [10], [13], [14]. One possible explanation for this equivocality may be in the propensity for PUFAs, of which ω-3 is a form, to oxidize. PUFAs tend to oxidize because of their large numbers of carbon–carbon double bonds and owing to the position of these bonds [15]. Aldehydes are a potential oxidation product. Aldehydes have been shown to have mutagenic, cytotoxic, immune system aggravating, and inflammatory properties in addition to direct injurious effects on endothelial cells that may contribute to many different disease processes [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37]. Therefore, it is important to determine whether oxidation is a common problem in commercially available ω-3 FA supplements.
Several existing studies have concluded that lipid peroxidation is indeed a common problem in ω-3 FA supplements [15], [20], [38], [39]. The oxidative state of oils has been commonly determined by measurement of the peroxide and anisidine values. Although these methods can determine the total amount of primary and secondary oxidation products, the composition of these lipid peroxides (LOPs) in terms of groupings of types of LOPs is undetermined by these methods. Because different aldehydes have distinct modes of action and various grades of reactivity, it is important to determine the type(s) of aldehydes present. Nuclear magnetic resonance (NMR) spectroscopy often is used to study chemical structures. 1 H NMR can be used to identify the carbon-hydrogen structures present in organic compounds, and thus the group of any aldehydes present [40]. As NMR is a very sensitive detection method, it is possible to detect very small concentrations that may not be detectable using other methods. Because even small amounts of aldehydes may be harmful [26], this study is of great importance. Therefore, we investigated the hypothesis that aldehydes are indeed present in many commercially available ω-3 FA supplements. The focus of this study was exclusively on commercially available EPA- and DHA-rich encapsulated ω-3 FA supplements because these are the most common mediums for their consumption. Because of resource constraints, it was not the purpose of this study to identify the exact molecular species present. That task falls to future studies. This work is of a pilot nature, thus we randomly selected and purchased 12 different oils over the counter from various local retailers according to the sales representatives’ recommendations. Further study is required to assess the prevalence of aldehyde contamination in commercially available ω-3 supplements more widely.
Section snippets
Materials
All reagents were purchased from Sigma-Aldrich (U.K.), unless otherwise stated. Twelve different commercially available encapsulated ω-3 FA supplements were analyzed in this study. All ω-3 supplements were within their use-by dates. The samples were fish, krill, or algae oils. The use of the NMR machine was negotiated with a local university professor.
Sample preparation
Oil capsules were incised at one end and the oil collected in a clean glass tube. We immediately transferred 200 µL of each oil to another clean
Results
A typical 1 H NMR spectrum of krill oil with magnifications of its 0.80 to 1.02 and 9.75 to 9.83 ppm regions is shown in Figure 1. ω-3 FAs give rise to a signal at 0.97 ppm, ω-6 FAs at 0.89 ppm, ω-9 and saturated fatty acids (SFAs) both appear at 0.88 ppm (Table 1 provides further details). The difference between these signals is due to the carbon–carbon double bond at the ω-3 position in the ω-3 FAs compared with the position of double bonds in other unsaturated FAs. Quantification of ω-3 as a
Disclaimers
The present study did not make any inferences with respect to purified EPA or DHA oil products because the samples were not purified (i.e., fish, krill, or algae extracts). The study did not make inferences with respect to products containing antioxidants, as none of the samples tested contained these. This study was of a pilot nature; as such, more data is needed to determine the prevalence of oxidation in commercially available ω-3 supplements more widely.
Krill oils
Three different groups of aldehydes
Conclusion
Of the 12 ω-3 supplements tested in this study, 75% two-thirds, (8/12) contained aldehydes. Aldehydes are potentially problematic owing to the risks for multiple types of adduct formation with biological molecules, leading potentially to inflammation, dysfunction, CVD, DNA damage, cancers, and a myriad of other health concerns. Krill oils tested in this study invariably contained aldehydes, and at relatively very high concentrations. Fish and algae oils contained aldehydes in four of the eight
Acknowledgment
The authors acknowledge Martin Grootveld for allowing access to the NMR spectrometer, his advice on data collection and interpretation, and access to comparative spectra.
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