Letters to the Editor |
Reply: Calcium homeostasis and anovulatory infertility
1 Department of Nutrition, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115, USA 2 Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA 3 Connors Center for Women's Health and Gender Biology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA 4 Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA 5 Department of Biostatistics, Harvard School of Public Health, Boston, MA, USA
6 Correspondence address. Tel: +1-617-432-4584; Fax: +1-617-432-2435; E-mail: jchavarr{at}hsph.harvard.edu
We read with interest the letter from Drs Farmakiotis, Katsikis and Panidis regarding our manuscript ‘A prospective study of dairy foods intake and anovulatory infertility’ (Chavarro et al., 2007a
).
As pointed out by the authors, we reported strong inverse associations between calcium and vitamin D intakes and the risk of anovulatory infertility that disappeared after BMI and other factors were accounted for in the analysis. We concluded that these results do not rule out the possibility that these nutrients are associated with anovulatory infertility in certain groups of women, for example, women carrying some genetic variants of the vitamin D receptor. They suggest that these nutrients could also be important determinants of PCOS manifestations, such as infertility, among overweight and obese women. Our findings are compatible with their interpretation. Unfortunately, our cohort may not be the best suited to test this hypothesis due to the low frequency of obesity among these women (10%).
We agree with the authors that the potential role of calcium homeostasis and vitamin D status on PCOS-associated reproductive morbidity should be further studied in future large-scale studies. We think that future studies examining these relations should measure, whenever possible, serum or plasma levels of 25(OH) Vitamin D. Sun exposure can be a more important source of vitamin D than foods or even supplements and fortified foods (Hathcock et al., 2007) providing >90% of the requirements for most people (Holick, 2004). Only considering dietary sources of vitamin D, as was the case in our report, is likely to misclassify vitamin D status and thus true effects of vitamin D on reproductive function may go undetected. A possible mechanism by which vitamin D status may influence ovulatory function is through its purported effects on insulin sensitivity. Lower vitamin D status has been associated with decreased insulin sensitivity (Martini and Wood, 2006) and insulin sensitizers are known to improve ovulatory function in women with PCOS (Azziz et al., 2001; Brettenthaler et al., 2004). Similarly, we have previously reported how lifestyle factors known to affect insulin sensitivity are also related to anovulatory infertility in the expected direction (Rich-Edwards et al., 2002; Chavarro et al., 2007b). These findings, as well as those mentioned by Farmakiotis et al. in their letter, point to the importance of studying the potential role of vitamin D and other dietary factors on fertility beyond the well described influence of body weight.
References
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Brettenthaler N, De Geyter C, Huber PR, Keller U. Effect of the insulin sensitizer pioglitazone on insulin resistance, hyperandrogenism, and ovulatory dysfunction in women with polycystic ovary syndrome. J Clin Endocrinol Metab (2004) 89:3835–3840.
Chavarro JE, Rich-Edwards JW, Rosner B, Willett WC. A prospective study of dairy foods intake and anovulatory infertility. Hum Reprod (2007) 22, a. 1340–1347.
Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Dietary fatty acid intakes and the risk of ovulatory infertility. Am J Clin Nutr (2007) 85, b. 231–237.
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