The research has potential important implications for enhancing calcium levels in the population, which have been falling in many countries as milk consumption decreases. Such decreases may have detrimental effects on bone health and increase the risk of osteoporosis, which is reported to affect approximately 9 million American adults. An additional 48 million have low bone mass, placing them at increased risk, according to data from the National Osteoporosis Foundation.
While many calcium-fortified products can be found on the market, formulators and nutritionists have not traditionally taken into account interactions between calcium and other dietary components, said researchers from the China Agricultural University in Beijing, Sichuan Agricultural University, Xi'an Jiaotong University, and the Chinese University of Hong Kong.
“For example, calcium ions have been reported to have a negative effect on iron and zinc uptake, because [the receptor] DMT1 located in the small intestinal is a common receptor for these divalent metal ions. Also, dietary factors such as tannins and oxalate greatly inhibit calcium uptake,” they wrote in the journal Bone.
“Thus a new class of Ca-enriched nutrient for the fortification of food which can overcome these shortcomings has the potential to improve calcium nutrition.”
The new study is the first time that edible protein cages have been used to encapsulate calcium ions, said the researchers, with each cage containing about 140 calcium ions.
The new study indicated that encapsulation of calcium in phytoferritin nanocages not only protected the mineral against tannic acid and oxalic acid, but also led to absorption by cells via a different pathway than seen with free calcium ions.
Tests using Caco-2 cells indicated that absorption did not occur via the DMT1 receptor as seen with free calcium ions, but occurred via a receptor called TfR1.
The researchers also noted that the complexes are suitable for vegetarians because of plant source.
“These findings indicate that the broad role of ferritin as a nanoplatform can play in the field of nutrition,” they wrote. “Exploration of a novel, alternative dietary calcium source with a different cell absorption mechanism may help improve calcium nutritional status and may prevent calcium deficiency problems.”
The potential economic benefits of boosting bone health with calcium (and vitamin D) were illustrated in a report from Frost & Sullivan and commissioned by the Council for Responsible Nutrition (CRN), with the data showing that supplements of calcium plus vitamin D for all US women with osteoporosis could provide healthcare cost savings of $1.08 billion per year.
Volume 64, Pages 115-123, doi: 10.1016/j.bone.2014.04.006
“A novel calcium supplement prepared by phytoferritin nanocages protects against absorption inhibitors through a unique pathway”
Authors: M. Li, T. Zhang, H. Yang, G. Zhao, C. Xu