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Soy is the major source of dietary exposure to isoflavonoids (IFLs). Accumulating evidence supports a role for soy and IFLs in the protection against many chronic diseases including cancer. After soy intake we found a biphasic IFL appearance pattern in plasma as well as in urine that we suggest to be due to IFL absorption in the small intestine (ca. 10%) during the first 2 h after intake and IFL absorption in the large intestine (ca. 90%) 4–6 h after intake. While each IFL disappears from the circulation at different times excellent correlations between urinary and circulating IFL values were discovered and algorithms to convert urinary excretion values into circulating levels were established. We suggest the term ‘apparent bioavailability’ when using urinary data to describe IFL exposure. The IFL bioavailability was found to be influenced by gut bacteria, oral antibiotic treatment (OABX), and an individual’s age and health status. While daidzein (DE) and genistein start to be absorbed minutes after intake, equol (EQ) appears in plasma only after a minimum of 8 h following soy intake owing to the required transit time of DE to the colon where the conversion of DE to EQ takes place by intestinal microbiota. We have also shown that the apparent IFL bioavailability is higher in children than adults, higher in healthy versus non-healthy individuals, and decreased in children but increased in adults during OABX. Finally, we propose to use a urinary EQ/DE ratio of 0.018 with a DE threshold to identify EQ producers. With this cutoff definition we observed that EQ production is inconsistent over time in 5–30% of both premenopausal and postmenopausal women.

More isoflavones appear in children than in adults after adjustment for isoflavone intake. Systemic isoflavone exposure in infants can be determined by urinary analysis.

Isoflavones (IFLs) are natural products to which humans have been traditionally exposed predominantly through soy foods; more recently humans are also exposed to them through soy protein addition to processed foods or through supplements. They are structurally similar to steroidal estrogens and can exert estrogenic or antiestrogenic effects depending on their concentrations and on the tissue considered. These properties qualify IFLs to be classified as phytoestrogens and are believed to account for many of the biological effects observed for soy and/or IFL exposure including benefits for bone and heart health or prevention of menopausal symptoms and certain types of cancer. In order to evaluate the function of IFLs, alone or when exposure happens through soy intake, pharmacokinetics and bioavailability are critical issues to be considered in epidemiologic and clinical research. For this purpose precise, accurate, robust, fast, and affordable techniques for IFL analyses are required.

The purpose of the present study was to determine whether children experience a higher systemic exposure to isoflavonoids when consuming a body weight-adjusted dose of soya compared with adults. Forty study participants were recruited from a local Waldorf school, including twentyone children and nineteen adults. Participants collected a baseline urine sample and ate immediately thereafter a body weight-adjusted dose of soya nuts (15 g/54·4 kg equivalent to 0·615 (SD 0·036) mg total isoflavones/kg) followed by a 12 h urine collection. Nineteen children and eighteen adults completed the protocol correctly (fourteen child-parent pairs). Children, compared with adults, showed a statistically significant (P,0·05 by unpaired t test) higher urinary isoflavone excretion rate for daidzein (þ 39 %), genistein (þ 44 %), all non-metabolites (daidzein þ genistein þ glycitein; þ41 %) and total isoflavonoids (þ 32 %). Isoflavones are more bioavailable in children v. adults. Urine is an excellent medium to determine systemic isoflavone exposure in children due to its non-invasiveness and high compliance, in particular when collected overnight; it also allows evaluation of completeness of specimen collection. Isoflavones: Soya: Children: BioavailabilityIsoflavones (IFL) are suggested to protect against many chronic diseases including breast, prostate and colorectal cancer, osteoporosis and cardiovascular disorders, as well as menopausal symptoms 1 -7 . IFL exposure occurs mainly by the diet through intake of soya products which contain typically a total of 0·01 -0·3 % IFL composed of mainly glycosides of genistein (GE), daidzein (DE) and glycitein (GLYE) (Fig. 1) 8 -11 . Strong evidence was provided recently that soya intake protects against breast cancer in adulthood 12 and, particularly, when consumed at early age 13,14 . Orally administered IFL are believed to be efficiently absorbed by diffusion through the mucosa after conversion of the glycosides to the bioavailable aglycone, which occurs mainly by intestinal bacteria 15 -20 . Urinary or plasma IFL were found to be reliable biomarkers for soya consumption 21 -27 , and urinary appearance of isoflavonoids reflect circulating levels accurately when timing of specimen collection is considered accurately 16,28 . While this is well researched in adults, little is known about the bioavailability of IFL in children 16 -18,29 . Relative to their mothers, urinary IFL excretion rate (UIER) was much lower in infants breast fed from soya-consuming mothers, but higher in babies eating tofu 28 . Urinary analysis revealed that children were more frequently able to convert DE to O-desmethylangolensin (DMA) or equol when they were raised on soya-v. cows' milk-based formula as infants, but this difference was apparent only at very young age and disappeared at age 3 -7 years 30 . In seven up to 4-month-old boys mean total plasma IFL concentrations were 3·7 mmol/l, 20 nmol/l and 16 nmol/l when fed soya-based formula, cows' milk-based formula, or breast milk, respectively. Urinary IFL c...

Background Computed tomography (CT) is an imaging modality involving ionizing radiation. The presence of γ-H2AX foci after low to moderate ionizing radiation exposure has been demonstrated; however it is unknown whether very low ionizing radiation exposure doses from CT exams can induce γ-H2AX formation in vivo in young children. Objective To test whether very low ionizing radiation doses from CT exams can induce lymphocytic γ-H2AX foci (phosphorylated histones used as a marker of DNA damage) formation in vivo in young children. Materials and methods Parents of participating children signed a consent form. Blood samples from three children (ages 3–21 months) undergoing CT exams involving very low blood ionizing radiation exposure doses (blood doses of 0.22–1.22 mGy) were collected immediately before and 1 h post CT exams. Isolated lymphocytes were quantified for γ-H2AX foci by a technician blinded to the radiation status and dose of the patients. Paired t-tests and regression analyses were performed with significance levels set at P<0.05. Results We observed a dose-dependent increase in γ-H2AX foci post-CT exams (P=0.046) among the three children. Ionizing radiation exposure doses led to a linear increase of foci per cell in post-CT samples (102% between lowest and highest dose). Conclusion We found a significant induction of γ-H2AX foci in lymphocytes from post-CT samples of three very young children. When possible, CT exams should be limited or avoided by possibly applying non-ionizing radiation exposure techniques such as US or MRI.

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More isoflavones appear in children than in adults after adjustment for isoflavone intake. Systemic isoflavone exposure in infants can be determined by urinary analysis.