Since no substantial global datasets of human stable isotope ratios are currently available, although the amount of available (published) data has increased within recent years, this article reports on a project that summarized the published data on human global δ13C andδ15N values (around 3,600 samples) and added experimental values of more than 400 additional worldwide human hair and nail samples; and In order to summarize isotope ratios for hair and nail samples, correction factors were determined.
Natural stable carbon (δ13C) and nitrogen isotope ratios (δ15N) of humans are related to individual dietary habits and environmental and physiological factors. In forensic science the stable isotope ratios of human remains such as hair and nail are used for geographical allocation. Thus, knowledge of the global spatial distribution of human δ13C and δ15N values is an essential component in the interpretation of stable isotope analytical results. The current available dataset of human stable isotope ratios is biased towards Europe and North America with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ13C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ15N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production. The current article notes that the available dataset of human stable isotope ratios is biased towards Europe and North America, with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ13C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ15N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production. There are still a large proportion of countries, especially in Africa, where there are no available data for human carbon and nitrogen isotope ratios. Although the interpretation of modern human carbon isotope ratios at the global scale is possible, and correlates with the latitude, the potential influences of extrinsic and/or intrinsic factors on human nitrogen isotope ratios have to be taken into consideration. (publisher abstract modified)