GLA increases the production of DGLA (hero) and AA (baddie), building products for eicasanoids, which in turn are building blocks for hormones. The DGLA:AA ratio is considered more important than absolute levels of either.
The controversy with GLA is how it affects that DGLA:AA ratio for production. Barry Sears of the Zone doesn't recommend GLA supplementation, because he believes it [I}eventually[/I] worsens the DGLA:AA ratio. However the studies I've read show that it improves the DGLA:AA ratio, even through a year.
EPA improves the DGLA:AA ratio, but it decreases overall DGLA and AA production. While absolute levels aren't important, you also get AA from the (animal) fat you eat and the stored fat you burn from your body.
The idea is to supplement GLA with EPA. How do you know how much GLA you need? Your skin.
Your skin has no receptors for AA, so AA levels do not directly affect your skin quality. However, low DGLA levels will dry out the skin, create spots, create wrinkles, etc. It is one marker of your DGLA health.
Right now, I'm working with 600mg GLA with 1800mg EPA. My concentration levels and mood swings are ridiculously terrific (need less sleep, level hunger), however I'm still dealing with occasional bouts of dry skin. I'm wary about increasing GLA any more, but I might give it a try.
cheers,
Jules