Here are two recent references on lowering of age at menarche.  Both point
to better and even "more than adequate" nutrition (obesity) as being the
major cause.

>UI  - 99347448
>AU  - Wattigney WA
>AU  - Srinivasan SR
>AU  - Chen W
>AU  - Greenlund KJ
>AU  - Berenson GS
>IN  - Tulane Center for Cardiovascular Health, Tulane School of Public
>      Health & Tropical Medicine, New Orleans, Louisiana 70112-2824, USA.
>TI  - Secular trend of earlier onset of menarche with increasing obesity
>      in black and white girls: the Bogalusa Heart Study.
>SO  - Ethnicity & Disease 1999 Spring-Summer;9(2):181-9
>AB  - Secular trends in onset of menarche and obesity were examined 14
>      years apart in two biracial (black-white) cohorts of girls aged 8 to
>      17 under study for cardiovascular risk. The first cohort (N=1,190,
>      64% white) was examined in 1978-1979, the second (N=1,164, 57%
>      white) in 1992-1994. The second cohort was heavier in terms of body
>      weight and Rohrer index (weight/height3) than the first (P<0.001),
>      except among black girls aged 12 to 13 years. Subscapular skinfold
>      thickness increased in the second cohort of all ages (P<0.0001),
>      while increases in triceps skinfold were less marked. The onset of
>      menarche occurred at an earlier age in the second cohort compared
>      with the first cohort (P<0.0001), both in black girls (11.4+/-1.3 vs
>      12.3+/-1.4 years) and white girls (11.5+/-1.3 vs 12.3+/-1.3 years).
>      Furthermore, twice as many girls in the second cohort had reached
>      menarche by ages younger than 12 years (P<0.001). All of these
>      obesity measures were significantly associated with the age of
>      menarche in both cohorts (P<0.001) adjusting for height, race and
>      age at examination. These results suggest that this secular trend
>      toward increasing frequency of early onset of menarche may be the
>      result of increasing obesity noted in girls of both races. Since
>      increases in body fatness and related early onset of menarche are
>      risk factors for disorders in adult life including cardiovascular
>      disease and breast cancer, the secular trend in the increasing
>      incidence of obesity throughout the United States is becoming a
>      major public health problem.
>LG  - English
>
>2
>UI  - 99266197
>AU  - Graham MJ
>AU  - Larsen U
>AU  - Xu X
>IN  - Department of Environmental Health, Harvard School of Public Health,
>      Boston, Massachusetts 02115, USA.
>TI  - Secular trend in age at menarche in China: a case study of two rural
>      counties in Anhui Province.
>SO  - Journal of Biosocial Science 1999 Apr;31(2):257-67
>AB  - There is increasing evidence that age at menarche has decreased in
>      Europe and the United States during the last century and in Japan
>      over the last several decades. Data from a community-based survey
>      conducted in two rural counties of Anhui Province in China indicate
>      a similar, downward secular trend in age at menarche for Chinese
>      women. The present study shows the mean age at menarche decreased by
>      2.8 years, from 16.5 to 13.7, over an approximate 40-year time
>      interval. This rapid decrease in age at menarche may partly be due
>      to better nutrition and living standards reflected by the improved
>      socioeconomic standards experienced in China over the past few
>      decades. To test this hypothesis, a number of determinants of age at
>      menarche were assessed; year of birth, literacy status, county of
>      residence, amount of physical labour, general health status,
>      pesticide exposure before age at menarche, and drinking water source
>      were all found to be associated with age at menarche.
>LG  - English
>

             ***********************************************
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(TM)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html