Choose greens wisely: AAS reveals calcium availability
- Published: Jan 15, 2015
- Author: David Bradley
- Channels: Atomic
Eat the right greens
An in vitro study using atomic absorption spectroscopy has investigated the concentrations of calcium found in diverse green vegetables commonly used in Indian cuisine as well as allowing the researchers to comment on the availability for absorption from the diet of the calcium present in these edible plants. The work perhaps points the way to defining which green vegetables are the more optimal dietary sources of calcium, which is particularly important for vegans and some vegetarians who do not obtain calcium from dairy products nor meat.
Chemists Augustine Amalraj and Anitha Pius of The Gandhigram Rural Institute - Deemed University, in Tamil Nadu, India, point out that calcium is the most abundant mineral element in the body, found in many foods but also ingested in supplement form. The majority of the body's calcium store is concentrated in tooth and bone. The balance between deposition and resorption of bone is keenly regulated by the body but control becomes looser as we age and in particular in post-menopausal women and in some disease states leading to bone deficit that can make breaks happen more readily. As such, ensuring a person has an adequate supply of dietary calcium throughout their lives can be critical to bone health.
Unfortunately, dietary sources of calcium are limited with a diet of mainly vegetables, for vegetarians and those in the developing world, for instance, where dairy products or meat are either not eaten out of choice or there is limited availability. As such, it is important to know which vegetables offer the best choice in terms of calcium intake. The team reports that green leafy vegetables represent an important component in the diet and provide a good source of many vitamins, minerals and phytochemicals beneficial to health. However, they also contain a complex array of natural products metabolites and other compounds that can reduce the bioavailability of calcium, for instance, oxalate, phytate, tannin and dietary fibre. After all, the plants themselves did not evolve to provide humans with a source of food and the complex biochemistry of all species exists for the benefit of the plant not those who eat it.
The team has now used a simulated gastric digestion method to break down samples of twenty green leafy vegetables commonly eaten in a typical Indian diet and the used AAS to measure calcium content and equilibrium dialysis to assess bioavailability of any calcium present. The team found that cooking made little difference to calcium bioavailability.
Testing times for greens
Among the plants tested, Sesbania grandiﬂora was particularly high in calcium absorption inhibitors despite containing high levels of calcium. By contrast, Chenopodium album, Alternanthera philoxeroides and Centella asiatica with their lower total calcium content, released almost twice as much calcium for absorption than other species. Fundamentally, absolute calcium content was not particularly relevant to the diet, rather the concentrations of inhibitors if high made a particular vegetable less beneficial for those hoping to boost their calcium intake.
The team concludes that people should be encouraged to eat more C. album, A. philoxeroides, C. asiatica, H. sabdariffa (Linn), A. dentata, B. alba and A. indica, which are all rich in bioavailable calcium and so can reduce malnourishment as well preventing the dental problem of ﬂuorosis by precipitating fluoride as insoluble calcium fluoride.
Food Chem 2015, 170, 430-436: "Bioavailability of calcium and its absorption inhibitors in raw and cooked green leafy vegetables commonly consumed in India – An in vitro study"
Article by David Bradley
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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