Well, I just read through the whole thing, and there's some issues with the study. We can say there's a correlation, but cannot assign causation from this study alone, anyways. For instance, while they questioned how often chocolate was eaten, they did not question the amounts, form, or purity of said chocolate. Moreover, "[a]fter adjustment for energy intake, daily chocolate consumers had significantly higher intakes of total and saturated fat, total carbohydrate, and sugar and lower intakes of protein, starch, fiber, and potassium." Another interesting sentence is this one: "In comparison to participants who rarely consumed chocolate (<1 time/wk), participants who consumed chocolate daily (≥1 time/d) had a significantly lower body weight and BMI and a higher socioeconomic status and total energy intake." Still, they did a good job analyzing the co-variant factors like BMI. However, D3 intake (or time in the sun) was not looked at, nor other supplementation. Also, I'd imagine they would have prohibited the women from taking such supplements in the first place as that would have affected their original purpose to study calcium supplementation on bone density.
Personally, I find it a bummer that they did not distinguish between the group that had been on the calcium supplements or the placebo (I was wrong about my earlier statement thinking that this was before the calcium supplement study), but put them both together, nor did they break down the two groups to show if calcium supplementation did anything either. I seriously feel they should have done that, and that we lose a lot of interesting data due to them not.
There is one possible mechanism chocolate could do it through, that oxalate, which can decrease calcium uptake. However, chocolate contains calcium, and in the study the study in question cited about oxalate, they show that oxalate did not affect the absorption of calcium from milk, it was only the cojugated calcium oxalate that was poorly absorbed, but which did not cross exchange with the milk borne calcium (see
here). This strongly implies that oxalate does not stop calcium from being absorbed in the diet, unless calcium oxalate is the only form of calcium you are taking in, then you'd only need to ingest higher amounts to gain the same amount of calcium as you'd get from lesser amounts of dairy calcium. So, only the calcium in the chocolate will be less readily absorbed than other sources of dietary calcium (except spinach calcium, which is even harder to absorb apparently), not to mention that even if there's enough free oxalate to strip calcium from other conjugated dietary calcium forms (which the above study suggest it doesn't readily do) they'd have to ingest the oxalate always at the same time as their other calcium intake source to limit it. This actually makes it seem even less likely that oxalate in chocolate (or chocolate itself, alone) is responsible for the observed effects, to me.
Here is a study looking in young women and caffeine sources on bone mass, where chocolate was one of the sources investigated. While their focus was on caffeine in the chocolate, they still found no significant decrease in bone mass in the chocolate eaters. So at least there's some counter evidence in the younger age group. Interestingly, caffeine was associated with slight bone mass loss, so that's something to think about, but it was not significant.
Anyways, I don't think you have much to worry about unless another study can come out and actually prove what's going on. Right now, we have a possible correlation, but far more questions than evidence. Something to keep an eye on.
Edited by geddarkstorm, 20 January 2009 - 06:01 AM.
