Veggies calcium
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Calcium Bioavailability in Vegetables: Key Insights
Introduction to Calcium in Vegetables
Calcium is a crucial nutrient for human health, playing a vital role in bone health and various biological processes. While dairy products are well-known sources of calcium, many vegetables also contain significant amounts of this essential mineral. However, the bioavailability of calcium from vegetables can vary widely due to the presence of certain inhibitory compounds.
High Oxalate Vegetables and Calcium Absorption
Certain vegetables, such as Chinese spinach and rhubarb, have high oxalic acid content, which significantly reduces calcium absorption. Studies have shown that the calcium absorption index is lowest for Chinese spinach (0.257) and rhubarb (0.235), while it is higher for vegetables like Chinese mustard greens and cabbage flower leaves (1.097). This indicates that oxalic acid is a major inhibitor of calcium absorption in these vegetables.
Inhibitory Factors Affecting Calcium Bioavailability
The presence of dietary fiber, phytate, and oxalate in vegetables can inhibit calcium absorption. For instance, vegetables like kale, celery, and Chinese cabbage, which have low levels of these inhibitors, show higher calcium dialysability (20-39%) compared to those with higher levels of inhibitors, such as sesame seeds and amaranth, which show much lower dialysability (2-7%). Similarly, in Indian green leafy vegetables, high levels of oxalates, phytates, and tannins were found to reduce calcium bioavailability significantly.
Brassica Vegetables: A Rich Source of Bioavailable Calcium
Brassica vegetables, including broccoli, bok choy, and kale, have been found to exhibit excellent calcium bioavailability. Studies indicate that the fractional calcium absorption from these vegetables is slightly higher than that from milk, with values around 0.514 compared to 0.463 for milk. This makes Brassica vegetables a highly recommended source of calcium.
Cooking and Calcium Bioavailability
Cooking does not significantly affect the bioavailability of calcium in green leafy vegetables. For example, in a study of 20 commonly consumed Indian green leafy vegetables, cooking did not alter the calcium bioavailability, which was primarily influenced by the content of oxalates, phytates, and dietary fibers.
Calcium Biofortification in Vegetables
Biofortification is an effective strategy to enhance the calcium content in vegetables. For instance, biofortified baby leaf vegetables like basil, mizuna, and endive showed a significant increase in calcium content without affecting their growth or quality. The bioaccessibility of calcium in these biofortified vegetables ranged from 25% to 40%, making them a viable option for increasing dietary calcium intake. Similarly, genetically modified carrots with elevated calcium transporter activity showed a 41% higher calcium absorption compared to control carrots.
Conclusion
Vegetables can be a significant source of dietary calcium, but the bioavailability of calcium varies widely depending on the presence of inhibitory compounds like oxalates, phytates, and dietary fibers. Brassica vegetables and biofortified vegetables offer excellent bioavailability and can be recommended as alternative calcium sources to dairy products. Understanding these factors can help in making informed dietary choices to ensure adequate calcium intake.
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