I have been taking 15 mg zinc twice a day, along with a multi that has ~20 mg, and have not yet gotten the flu or any intense illness this winter. I've had ongoing low grade illness almost constantly, though. Still, I want to decrease it to just 15 mg /day and see how that goes. I don't take extra copper, although there is some in the multi, and I don't want things to get too out of balance.
Magnesium -- A few years ago I had bad muscle pains a lot, sore muscles that would last for days, migraines very often, etc., after the combo of B-12 deficiency and thyroid implosion, and those worsened in the winter. I had started taking a multi-mineral by Rainbow Light and then went on a Christmas break to stay with my husbands parents and forgot to bring it. I didn't think much of it, but my body went ballistic -- terrible muscle pains and extreme anger and depression, and trapped in Middle Georgia with no way to alleviate any of it. On the way back to the West Coast my flight got stuck in Salt Lake City and they (Delta) said it would be 2 days to get onto another flight, so I paid $250 just to get out of there via another airline because of the horrible state I was in.
That was how I learned I needed magnesium because it didn't show up as deficient on the Spectrocell labs I had done, before I was taking any multi-mineral.
So I started on a multi-month trial of several different brands because I very quickly found that magnesium drove my gut wild -- I would have cramps in my lower back and sides so intense that I had to take ibuprofen every day, and sometimes would have to stay home from work. I was trying to do a slightly larger ratio of Mg than Calcium, or even ratio, but that was too difficult, so I gave up on that. I did some research and found this woman's website, which was very helpful --
http://www.krispin.com/magnes.html
So I saw that she recommended some types developed to *not* interact with the gut. She says:
The medical community repletes magnesium by giving 400 mg. of oxide, sulphate or gluconate 4-6 times a day. At this level diarrhea becomes a problem and a loose stool depletes magnesium and other electrolytes quickly.
Albion Labs chelated magnesium is designed to deliver magnesium without diarrhea. Even when using the Albion chelate a loose stool can still be a problem under certain circumstances. Pathogenic gut bacteria have the ability to 'unchelate' any form of magnesium so that it too may contribute to diarrhea. If you have any type of gut issues consider testing for pathogens and treating before adding back magnesium. You should discontinue magnesium if your stool becomes soft or un-formed.
So I tried the Albion labs version by Carlson, and it worked, but I can only take a 1/2 size pill (50 mg) or its really over stimulating --
http://www.iherb.com/Carlson-Labs-Chelated-Cal-Mag-180-Tablets/13463
It made a huge difference for me. These days I rarely get migraines, and the muscle pain I get is now different, I don't think due to magnesium, and still very much a problem, not improving.
I had planned on increasing the magnesium, but that's gone by the wayside lately with too many other issues cropping up. As it is I cannot even work 2 days in a row without become non-functional or sick.