Lucy, This paper states that formula-feeding leads to greater body fat 
which leads to earlier menarche: "Formula feeding in infancy is associated 
with adolescent body fat and earlier menarche.Novotny 2003" You could 
click "related papers" in PubMed....

There are plenty of papers that demonstrate link between higher weight and 
earlier puberty --- too many to mention.

This paper shows that age of menopause is reduced (in their sample of 150) 
by 7 years by having been breastfed: "Associations with age at natural 
menopause in Blackfeet women.Johnston 2001"

When researching for this article I wrote in 1999 ( 
http://www.babyreference.com/EarlyPuberty.htm ) I found plenty of articles 
providing epidemiological suggestions where regions with greater 
breastfeeding have later puberty --- from nation to nation as well as from 
industrializing urban areas versus rural areas of same nation. I'm sure 
you could find some. There are one or two referenced in this article. 
Below is just one (not best) example that popped up for me with quick look:

This paper shows that Asian populations with more breastfeeding have 
earlier menarche: Menstrual and reproductive factors and risk of breast 
cancer in Asian-Americans. Wu 1996

linda

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