For sometime now I've suffered from very soft nails.

I was pulling my trousers up yesterday and bent back one of my finger
nails.  It hurt a lot.  I decided to investigate what might be causing
the problem.  A few minutes searching Google found several pages
suggesting I may suffer from a Magnesium deficiency.

I have bought some Magnesium tablets.

During my research I found this:
http://www.hopkinsmedicine.org/press/2002/APRIL/020425.htm.

'Johns Hopkins scientists have found that simply increasing manganese
in cells can halt HIV's unusual ability to process its genetic
information backwards, providing a new way to target the process's key
driver, an enzyme called reverse transcriptase.

By measuring DNA produced by a related reverse transcriptase in yeast,
the Hopkins team discovered that higher than normal levels of
manganese, caused by a defective gene, dramatically lowered the
enzyme's activity. The scientists then proved that HIV's reverse
transcriptase responds to manganese in the same way.

Hopkins graduate student Eric Bolton determined that the defective
gene is PMR1, whose protein carries both manganese and calcium out of
cells. Using special yeast developed by others at Hopkins, he
discovered that manganese stops reverse transcriptase, the team
reports in the April 26 issue of Molecular Cell."