Alright, I'm thoroughly confused. I keep seeing sources that say any calcium powder made from ground oyster shell is bad and the only calcium supplement that is digestible is pure calcium carbonate— in other words, Zoo Med's calcium supplement is the only digestible supplement on the market. However, these sources are usually at least 5 years years old. Are these claims outdated, or have I just been misinformed all this time?
I would ask them for sources...
Calcium from sources like shells, egg shells and bones are typically useful to the body. Some sources more, some less and other minerals/nutrients play a role but I don’t think oyster shell is significantly less effective than pure calcium carbonate.
Elemental calcium doesn’t expire, it’s inert. Other vitamins like D3 and those used in multivitamins can decay over time, especially when exposed to air, heat, light and moisture.