Beliefs that extra exogenous oestrogens or anti-oestrogens can
prevent hormone-dependent cancers are often based on evidence from case
controlled trials like this assessment of dietary soya intake and
endometrial cancer risk by Zu and colleagues.1 Randomised controlled
trials have shown that such observational evidence for prevention of
cancers or vascular diseases can be wrong. Most of the categories in Table
3 and Table 4 show no statistically significant differences in endometrial
cancer risk with soya intake. When the data is adjusted only for age, only
one category, a middle intake of fresh soya beans, gives a reduced risk
estimate but higher intakes do not. When the same data is adjusted for
ten other confounders, including previous oral contraceptive use, higher
intakes of soya food fibre, soya protein and fresh soya beans apparently
reduce the risk significantly. In Table 4 only larger women with the
highest soya protein intakes seem to be protected but excess intake of
oestrogens can cause weight gain. It would be safer for heavier women to
lose weight than to take extra phytoestrogens. High soya intake can raise
copper levels, stimulate breast and fibroid growth and cause menstrual
bleeding. Even a two-week dietary supplementation of soy can have an
oestrogenic effect on the breast.2
Dramatic increases in breast cancers have matched fluctuations,
mostly increases; in the use of exogenous hormones in Western countries
promoting such use.3,4 Oestrogen use increases the risk of endometrial
cancer up to 12 times. Countries like Japan and China have had a low
incidence of breast and endometrial cancer, mostly because fewer women
have used oral contraceptives or hormone replacement therapy than in
Western countries. However, hormone dependent cancers are even less common
in some other countries, for example Ghana, where women do not consume
large amounts of soya. There maybe great financial pressures to convince
women of benefits of phytoestrogens but better evidence is needed to
allay fears of the dangers of extra hormone intake for any women and
especially for those who are already at higher risk because of previous
hormone use.
1.Xu W H, Zheng W, Xiang WB, et al. Soya food intake and risk of
endometrial cancer among Chinese women in Shanghai: population based case-
control study BMJ 2004;328:1285 (29 May), doi:10.1136/bmj.38093.646215.AE
(published 10 May 2004)
2.Hargreaves DF, Potten CS, Harding C, et al. Two-week dietary soy
supplementation has an estrogenic effect on normal premenopausal breast. J
Clin Endocrinol Metab. 1999;84:4017-24.
Rapid Response:
Soya intake and endometrial cancer risk.
Beliefs that extra exogenous oestrogens or anti-oestrogens can
prevent hormone-dependent cancers are often based on evidence from case
controlled trials like this assessment of dietary soya intake and
endometrial cancer risk by Zu and colleagues.1 Randomised controlled
trials have shown that such observational evidence for prevention of
cancers or vascular diseases can be wrong. Most of the categories in Table
3 and Table 4 show no statistically significant differences in endometrial
cancer risk with soya intake. When the data is adjusted only for age, only
one category, a middle intake of fresh soya beans, gives a reduced risk
estimate but higher intakes do not. When the same data is adjusted for
ten other confounders, including previous oral contraceptive use, higher
intakes of soya food fibre, soya protein and fresh soya beans apparently
reduce the risk significantly. In Table 4 only larger women with the
highest soya protein intakes seem to be protected but excess intake of
oestrogens can cause weight gain. It would be safer for heavier women to
lose weight than to take extra phytoestrogens. High soya intake can raise
copper levels, stimulate breast and fibroid growth and cause menstrual
bleeding. Even a two-week dietary supplementation of soy can have an
oestrogenic effect on the breast.2
Dramatic increases in breast cancers have matched fluctuations,
mostly increases; in the use of exogenous hormones in Western countries
promoting such use.3,4 Oestrogen use increases the risk of endometrial
cancer up to 12 times. Countries like Japan and China have had a low
incidence of breast and endometrial cancer, mostly because fewer women
have used oral contraceptives or hormone replacement therapy than in
Western countries. However, hormone dependent cancers are even less common
in some other countries, for example Ghana, where women do not consume
large amounts of soya. There maybe great financial pressures to convince
women of benefits of phytoestrogens but better evidence is needed to
allay fears of the dangers of extra hormone intake for any women and
especially for those who are already at higher risk because of previous
hormone use.
1.Xu W H, Zheng W, Xiang WB, et al. Soya food intake and risk of
endometrial cancer among Chinese women in Shanghai: population based case-
control study BMJ 2004;328:1285 (29 May), doi:10.1136/bmj.38093.646215.AE
(published 10 May 2004)
2.Hargreaves DF, Potten CS, Harding C, et al. Two-week dietary soy
supplementation has an estrogenic effect on normal premenopausal breast. J
Clin Endocrinol Metab. 1999;84:4017-24.
3. Grant ECG. Increases in breast cancer incidence.
http://bmj.com/cgi/eletters/328/7445/921#55298, 1 Apr 2004
4. Grant ECG. Authors' reply.
http://bmj.com/cgi/eletters/328/7445/921#55843, 6 Apr 2004
Competing interests:
None declared
Competing interests: No competing interests