Although it may seem like they controlled and compensated for everything, BA is right: correctional or association is not the same as causation.
Because I think examining scientific studies is interesting, I'm going to spend a little time talking about that, but since that may be long and boring for many of you, I want to say this first. There are constantly studies coming out that say certain things are good or bad for you. But compiled they mostly look like: Substance A is good for Organ B, but bad for Organ C, but in moderation is probably more good than bad, and moderate is less than quantity D unless you are a woman in which case it is less than quantity E. Oh and by the way, if you eat/use Substance F none of the above applies.
So I look at it like this: if it were possible to eliminate all cancer and disease (leaving only accidents/violence as potential cause of death) by eating MagicJuice and ONLY MagicJuice, for the rest of your life, BUT MagicJuice tasted like the most appalling thing in the world to you and skipping even one dose of MagicJuice or eating one thing besides MagicJuice would void its protection, would you do it? I personally wouldn't. Yes, I want to live a long happy life. But an overly restrictive diet would not qualify as happy for me. So I read the literature because its interesting, but if a change would make me feel deprived I don't bother. Because even MagicJuice won't protect you from getting hit by a bus.
And now, long potentially boring scientific stuff.
============================================
I pulled the abstract for the actual scientific article in question (
http://cjasn.asnjournals.org/content/6/1/160.short). Unfortunately it was published in a rather obscure journal, so I don't have access to the full article (I have access to 4 different university libraries and so this is a rarity for me!)
However, even from the abstract I see one big problem with your conclusion that artificial sweetner causes kidney function: the study doesn't examine the use of artificial sweetner, it looks specifically at artificially sweetened soda. In fact, this is the articles conclusion from the abstract:
Consumption of ≥2 servings per day of artificially sweetened soda is associated with a 2-fold increased odds for kidney function decline in women.
While the abstract suggests that sugar soda did not have an effect on their measured outcomes, without actually reading through the actual article it is difficult to fully evaluate. Further complicating this particular issue is this study:
http://www.nature.com/ki/journal/v77/n7 ... 9500a.html It looks at the effect of sugar-sweetened soda on kidney disease. What does it find? Well, unfortunately its not as simple as sugared soda does or doesn't lead to an increased risk of kidney disease.
From the paper:
Our findings are consistent with previously published reports in which high sugar-sweetened soda consumption was associated with prevalent hyperuricemia and renal injury
So it causes kidney disease, right?
Also from the paper:
Yet this study, to the best of our knowledge, is the first to examine whether sugar-sweetened soda consumption is associated with incident forms of these diseases. The results of these incidence analyses add an important note of caution to the literature on sugar-sweetened soda and HFCS. Although the cross-sectional analyses performed in this and other studies4, 19 support a hypothesis that increased HFCS-sweetened soda consumption leads to higher uric acid levels that in turn induce renal damage, the longitudinal analyses do not support this theory.
So actually depending on how you analyze the data, you get two different answers. This particular paper cites a dozen or so other studies participating in the "is sugared soda bad for kidneys" debate and concludes with this very telling remark:
Therefore, our findings add to but in no way close the heated discussion over the potential dangers of sugar-sweetened soda.
And to me a version of the above quote could be added to the end of just about any scientific article dealing with nutrition. Because data is data - but so much goes into experimental design, execution, analysis and interpretation, that two excellent researchers can get sound but different results from well-executed experiments. No one actually has to make a mistake to get a result that doesn't well represent the Absolute Truth. And since we can't really know what the Absolute Truth is, we end up with heated debate and a constantly changing knowledge base.
[/quote]