Rachel A. Gooze, the lead researcher in the current study which was published in the Journal of Pediatrics, thought that added incentive might be needed to encourage parents to help their children stop using bottles at a much easier age. Apparently, children should be off bottles by 12 to 14 months, which is when they should start using cups or sippy cups. It is interesting to note that, of all the "test subjects" in this study, one in five kids were still using a bottle by 24 months.
I saw no specification as to what was in the bottle, but I guess that matters rather a lot! The study author speculated that children may be getting too many calories through bottle feeding, but that wouldn't be the case if the children were getting breast milk or water through bottles. I personally have no experience with this, because neither of my children ever used bottles of any kind. We breastfed exclusively for the first six months and than started with baby-led weaning. When they were ready to start drinking fluids other than breast milk, my children used plastic "glasses". My daughter used a sippy cup for a while.
The researchers in this study did say that they were not sure of any direct link between bottles and obesity. Some other possibilities come to mind. For instance, formula is more likely to lead to obesity than breastfeeding, and parents who formula feed might be encouraged to start solids earlier too by their pediatricians. And early solids were already linked to obesity in an earlier study (new study warns against early solids for babies).