There are tests for things like prostate cancer that show up in the blood, and I believe there is a test available in USA for studying the gene base - very expensive indeed!
I would advise not to worry and to eat as healthily as you can, like
here, take moderate excercise and reduce your worry factor. In fact I couln't suggest a better outlook on life than
this one just posted by Nice-1.
As far as genetic markers are concerned, it has been found that genes can be switched on and off by the foods you are eating. It is a fairly new branch of biochemistry called
Nutrigenomics, and
see here and
Geoff Bland is at the head of a research organisation which is testing the various food functions, but if you google it you'll find all sorts of very learned papers on the subject!!.
Epigenetics is another slightly different study that looks at how a wider range of factors can influence genetic expression.
There is so much going on out there in scientific biochemical research and we are only just beginning to understand what's happening - there are exciting times ahead! I believe Functional Medicine is the medicine of the future - see the
Institute for Functional Medicine.
Meanwhile have fun and enjoy life - whatever it has to offer

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