背景:临床和生化维生素B12(B12)缺乏低于预期的素食者。外部吸收,比如从结肠,以及减少每日排泄,可能是维持B12稳态与边际摄入量的适应性机制。
目的:为了测量小肠和大肠对B12的吸收,以及它每天从体内排泄的速度,使用[13C]-氰钴胺示踪剂。
方法:在正常参与者中施用[13C]-氰钴胺示踪剂(2.5μg)后12小时内测量口服B12生物利用度。通过将[13C]-氰钴胺(5μg)直接滴入升结肠评价结肠B12的生物利用度。从血浆中示踪剂外观的2室建模计算生物利用度。在口服给药(5μg)后4周内,从体内消除[13C]-氰钴胺来测量B12的排泄率。
结果:口服B12生物利用度(n=11)在12小时内测得为63%±10%。晚期吸收峰,占吸收的12%,在给药的平均滞后时间为8.7h后观察到。结肠B12的生物利用度(n=10)在4小时内为7%±5%。每天的B12排泄率(n=4)为0.7±0.2μg/d。这些参与者中B12的最低每日需求量为1μg/d。
结论:B12在人结肠中被吸收。这一观察结果证实了结肠在每日B12营养治疗中的潜在贡献,以及可能较低的要求,可以解释在有边缘B12摄入量的人群中没有临床缺乏。
背景:本研究已在印度临床试验注册中心(CTRI)注册,注册号为CTRI/2018/04/012957,可从https://ctri获得。nic.在/临床试验/展示。php?mid1=49319&EncHid=&userName=029108。
Clinical and biochemical vitamin B12 (B12) deficiency is lower than anticipated in vegetarians. Extraileal absorption, such as from the colon, as well as reduced daily excretion, may be adaptive mechanisms to maintain B12 homeostasis with marginal intakes.
To measure the absorption of B12 from the small and large intestine, and its daily rate of excretion from the body, using a [13C]-
cyanocobalamin tracer.
Oral B12 bioavailability was measured over 12 h after administration of [13C]-
cyanocobalamin tracer (2.5 μg) in normal participants. The colonic B12 bioavailability was evaluated by direct instillation of [13C]-
cyanocobalamin (5 μg) into the ascending colon. Bioavailability was calculated from 2-compartmental modeling of the tracer appearance in plasma. The excretion rate of B12 was measured from [13C]-
cyanocobalamin elimination from the body over 4 wk after oral dosing (5 μg).
The oral B12 bioavailability (n = 11) was 63% ± 10% measured over 12 h. A late absorption peak, accounting for 12% of the absorption, was observed after an average lag time of 8.7 h from dosing. The colonic B12 bioavailability (n = 10) was 7% ± 5% over 4 h. The daily B12 excretion rate (n = 4) was 0.7 ± 0.2 μg/d. The minimum daily requirement of B12 in these participants was derived at 1 μg /d.
B12 is absorbed in the human colon. This observation confirms the potential contribution of the colon in daily B12 nutriture, and along with a possible lower requirement, could explain the absence of clinical deficiency in populations with marginal B12 intakes.
This study was registered in Clinical Trials Registry of India (CTRI) with the registration number CTRI/2018/04/012957, available from https://ctri.nic.in/Clinicaltrials/showallp.php?mid1=49319&EncHid=&userName=029108.