Abstract
Stable isotopes have been used as tracers in human nutritional studies for many years. A number of isotopes have been used frequently to assess body composition, energy expenditure, protein turnover and metabolic studies in general, such as deuterium (2Hydrogen), 18Oxygen, 13Carbon and 15Nitrogen. Nevertheless, there is still occasional confusion and concern over their safety, which can hinder the appropriate use of these isotopes in human studies. This mini review aims, therefore, to consider the safety of the four stable isotopes mentioned above, and to reiterate and reaffirm their safety once again. It is hoped that these data will be of use to new researchers in the field, as well as those considering the ethical or other implications of using these stable isotopes in nutritional research. Undoubtedly some of the confusion arises as deuterium, especially, is associated with the nuclear industry. However, as their name implies, of course, none of these stable isotopes are radioactive, and no adverse biological or physiological effects have been reported at the very low levels of enrichment that are used in human studies. There are ample data to reaffirm the safety of stable isotopes at the levels used in nutritional research, and unnecessary concerns and/or confusion should not be a block to continued use of these important tracers.
Highlights
It is hoped that these data will be of use to new researchers in the field, as well as those considering the ethical or other implications of using these two stable isotopes in nutritional research
No biological and/or physiological effects have been found when using 18O, 13C and 15N even at extremely high levels of enrichment far above those required in human nutritional tracer studies [14, 15]
Whilst adverse effects when using high enrichments of deuterium [6] have been described, once again the enrichment required to cause physiological changes are far in excess of those required for biological studies [12]
Summary
At the time of writing, it is 100 years since Francis Aston born in Birmingham in the United Kingdom, but working at the renowned Cavendish Laboratory in Cambridge, described the evidence, at that time, that neon consisted of mainly two isotopes that were stable and were not radioactive. Importantly, levels of enrichment that are associated with such side effects or death, are not required for the usual uses of deuterium to measure total body water, or in its other roles, such as in the doubly labelled water method for measuring total energy expenditure, or for assessing breast milk intake in infants. This was elegantly explained as far back as 1979, when one the most respected researchers in this area, WA Coward based in Cambridge, United Kingdom, responded to a letter in the Lancet seeking assurance that using deuterium in young infants was not a safety concern [12]. The capacity to increase the body pool safely with 15N has been described as “virtually limitless” [7]
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