Many supplements claim to contain ingredients like zinc, but a quick view of the label's ingredients will reveal they contain very little active ingredient. Some companies selling online make it very difficult for consumers to see the actual amount of active ingredient contained in their supplements. We believe vitamin companies need to be more transparent about this.
For example, most clinical studies examining the therapeutic benefit of zinc in fighting cold and flu in adults have shown therapeutic benefit from zinc doses above 75mg of elemental zinc per day, but some immune health supplements will claim to contain zinc despite elemental zinc content of 5mg or less per dose). So how much zinc should supplements contain? Some clinical trials suggest that elemental zinc content of 30-45mg per day is beneficial in preventing respiratory infections.
You can read more about zinc on The Science and ingredients page (all the above facts are referenced there!).