Magnesium gluconate
Magnesium gluconate is a compound with formula Mg2. It is the magnesium salt of gluconic acid.
According to one study, magnesium gluconate showed the highest level of bioavailability of any magnesium salt which implies its viability as a supplement, although of the 10 salts studied, all increased magnesium levels significantly. This study did not include magnesium glycinate, which is one of the most bioavailable forms of magnesium.
It has E number "E580".