Epidemiology of isoflavone intake

There are observed differences in incidence of cardiovascular disease, cancers and osteoporosis between population groups. Genetics, diet and lifestyle factors are all thought to be involved in the aetiology of these diseases, however epidemiological studies suggest that incidence of these "Western diseases" is inversely related to phytoestrogen consumption ²⁷. For instance, the total isoflavone intake is estimated to be highest in Japanese populations at 40 mg per day ²⁸ and in other Asian communities, this value has been calculated as 25-45 mg/day.

Epidemiological data indicate that Asian and particularly Japanese women have lower rates of osteoporosis, fractures, and cardiovascular disease than their Western counterparts who, on average, consume only 2-5 mg/day total isoflavones. Thus, attention has focused on the use of these plant-derived compounds as a method of alleviating menopausal symptoms and maintaining cardiovascular and bone health throughout post-menopausal life.

Reduced menopausal symptoms
While every woman experiences menopause, not every woman experiences adverse symptoms of menopause. This is highlighted by the reported experience of women with acute symptoms in Asia versus other countries:

• 85% of women in America ²⁹
  
  
• 70-80% of women in Europe ^30,31
  
  
• 57% of women in Malaysia ³²
  
  
• 25% of women in Japan ²⁹
  
  
• 18% of women in China ³³
  
  
• 14% of women in Singapore ³⁴

It is well known that a diet which is low in fat and high in complex carbohydrates derived from grains, fruits, and vegetables, is associated with a lower risk of chronic diseases. However, epidemiological studies now indicate a role for diet in reducing menopausal symptoms, particularly an Asian diet which is abundant in isoflavonoid phytoestrogens ^35,36.

Cardioprotective
The lower incidence of cardiovascular disease in Asian countries compared to Western countries, suggests that isoflavones may be cardioprotective (Figure 3). Similarly, there is a lower incidence in vegetarians, whose protein source is mainly from isoflavone rich foods, compared to omnivores ^27,37.

Figure 3. Coronary artery deaths and isoflavone intake in different countries^27,37.

Reduced incidence of hormonal cancers
Hormone dependent cancer rates also vary markedly between regionally diverse populations. Migrant studies indicate that this is largely due to environmental factors, rather than genetics ³⁷. Epidemiological evidence suggests that a major environmental contributor to this effect is the traditional diet of Asian populations which confers a lower risk of hormone dependent cancers such as breast, ovarian and uterine ^38,39. Table 3 demonstrates the low incidence of breast cancer rates in Asian compared to Western populations. Several studies have observed a link to dietary intake of isoflavones. In a case-control study, an increased breast cancer risk was strongly correlated with a low intake of isoflavones, as measured by urinary isoflavone excretion ⁴⁰. A similar association was reported in a case-control study in Singapore, and a study of Asian-Americans consuming isoflavone rich foods ⁴¹. Isoflavones are a dietary factor of particular interest when considering hormone-related cancers due to their ability to act as selective oestrogen receptor agonists, antagonists as well as their anti-carcinogenic biological activities.

Table 3. Breast cancer incidence in populations (adapted from Reference 38)

Osteoporosis
Incidence of osteoporosis and osteoporotic fractures varies among populations, with a lower incidence in Asian compared to Western countries ²⁷. However, the lower rate of osteoporotic fractures seen in, for example Japan, is paradoxical, since Japanese have a lower peak bone mass, a lower lifetime exposure to oestrogen and a lower calcium intake compared to Western populations. Several factors have been proposed to explain the lower fracture rates observed in Asia. Lifestyle differences may offer some explanation. Physical activity such as sitting on the knees in the fully flexed position and frequent standing up in Japan is thought to develop hip musculature, as well as agility and balance. Also, it is proposed that due to cultural differences a greater proportion of the elderly population in Japan have adopted a lifestyle with restricted physical mobility which therefore reduces fracture rates ⁴². It has also been suggested that intake of isoflavones in the Asian diet prevents bone loss in post-menopausal women through their estrogenic action ³⁷.

» Go to Full Reference List