Pre-menopausal women with the highest average intakes of folate from the diet are at a 40 percent reduced risk of developing breast cancer, according to new findings published in the American Journal of Epidemiology.
The study was conducted with women in China where there was no mandatory fortification of flour with folic acid, the synthetic form of folate, during the course of the study. In the US, grain products have been fortified with folic acid since 1998.
As a result, only 13 percent of the Chinese women had folate levels that matched or exceeded the US recommended dietary allowance, wrote researchers from Vanderbilt University in Tennessee and the Shanghai Cancer Institute.
“Thus, it is possible that the […] relation with folate intake among premenopausal women may be due to a difference in folate insufficiency versus sufficiency.
“In support of this possibility, the present study appeared to have a threshold effect for folate intake that was achieved between the first and second quintiles of intake, with no added benefit beyond that level,” they added.
Not all good?
The researchers also report – for what they claim to be the first time – that niacin may be associated with an increased risk of hormone-sensitive breast cancer. They called for other studies to evaluate this link in more detail.
Over one million women worldwide are diagnosed with breast cancer every year, with the highest incidences in the US and the Netherlands. China has the lowest incidence and mortality rate of the disease.
Hormone-sensitive estrogen-receptor (ER) positive and progesterone-receptor (PR) positive tumors are said to be the most common type diagnosed among breast cancer patients in the US. These tumors are stimulated to grow by the female hormones estrogen and progesterone.
Data from Shanghai Women's Health Study (1997–2008) for 72,861 participants aged between 40 and 70 was used to assess potential relationships between intakes of folate, niacin, and vitamin B6 and B12 and incidence of breast cancer.
During the course of the study 718 cases of breast cancer were diagnosed. After crunching the numbers, the researchers report no link between vitamin B6 and B12 intakes and the risk of breast cancer in both pre- and post-menopausal women.
Only folate intake was associated with a reduced risk of breast cancer and this was limited to premenopausal women. Specifically, average intakes of 404 micrograms per day were associated with a 42 percent reduction in the risk of breast cancer, compared with average intakes of 194 micrograms per day.
On the other hand, average intakes of 17.6 milligrams per day of niacin (vitamin B3) were associated with a 60 percent increased in the risk of hormone-sensitive breast cancer, compared with average niacin intakes of 11.7 milligrams per day.
“Because of niacin’s involvement in steroid hormone synthesis, and ER+/PR+ breast cancer is hormone dependent, it is possible that niacin could accentuate estrogen synthesis and then, in turn, cancer progression,” wrote the researchers.
“However, to our knowledge, no study has evaluated niacin intake and breast cancer according to ER/PR status; therefore, further studies are needed to understand a possible mechanism.”
Source: American Journal of Epidemiology
2011, Volume 173, Issue 10, Pages 1171-1182, doi: 10.1093/aje/kwq491
“Dietary B Vitamin and Methionine Intakes and Breast Cancer Risk Among Chinese Women”
Authors: M.J. Shrubsole, X.O. Shu, H.-L. Li, H. Cai, G. Yang, Y-T. Gao, J. Gao, W. Zheng