RE: “DIETARY PROTEIN INTAKE AND EARLY MENOPAUSE IN THE NURSES’ HEALTH STUDY II”

RE: “DIETARY PROTEIN INTAKE AND EARLY MENOPAUSE IN THE NURSES’ HEALTH STUDY II” The recent study by Boutot et al. (1) will be of interest to those working in the field of bone health, as early menopause is a key risk factor for osteoporosis. New knowledge on lifestyle factors that might help prevent the condition is of value to women who may be at risk and to those involved in providing advice. Ceasing smoking and increasing physical activity are clear recommendations that are easy to understand, whereas nutritional factors and the concept of a healthy diet often appear inconsistent and vague by comparison. Current advice by the US Department of Agriculture provides examples of diets that would meet guidelines for healthy nutrient intakes (generally diets low in saturated fats and rich in fruit and vegetables) (2), but there is room for refinement. It is important to understand which nutrients and dietary factors might be the drivers behind any observed relationship with a particular health outcome. It is difficult to undertake dietary intervention studies, as changes in one food group or nutrient can affect others if energy intakes are to remain constant. Epidemiologic studies involving large numbers of women, such as the Nurses’ Health Study (http://nurseshealthstudy.org/), are useful, although any associations observed may prove not to be causal. The report by Boutot et al. (1) suggests that intake of vegetable protein is associated with reduced risk of early menopause. We would add a word of caution in highlighting “vegetable protein” together with a recommendation of servings per day of protein-rich foods, as one might be led to believe that this applies to foods such as nuts and soy protein. The authors found that the foods behind the association were pasta, dark bread, and cold cereal (1); these are usually thought of as carbohydrate-rich foods rather than sources of protein, and they also provide minerals and B vitamins. Could the authors clarify whether “cold cereal” refers to processed breakfast cereals (which are often fortified with vitamins and eaten with milk)? A recent study involving the same population showed that intakes of vitamin D and dairy foods were associated with a reduced risk of early menopause (3). Although there may have been good reasons to explore these dietary factors separately from the protein relationship, these individual analyses can build up a confusing picture of which factors are important. Both analyses corrected for the alternative factors, so we know that they are independent predictors, although in both cases the alternative study was not referenced. We request that Boutot et al. provide the effect sizes and confidence intervals for both factors included in the same model, so that readers are clear about their relative importance. Further, we would ask that they consider the use of data reduction techniques (e.g., principal components analysis) to produce dietary patterns. The results of dietary pattern analysis conducted using this large data set could provide a clear dietary message for reducing the risk of early menopause and could assist policy-makers in producing more focused dietary recommendations in the future. Acknowledgments Conflict of interest: none declared. References 1 Boutot ME , Purdue-Smithe A , Whitcomb BW , et al. . Dietary protein intake and early menopause in the Nurses’ Health Study II . Am J Epidemiol . 2018 ; 187 ( 2 ): 270 – 277 . Google Scholar CrossRef Search ADS PubMed 2 US Department of Health and Human Services; US Department of Agriculture . Dietary Guidelines for Americans 2015–2020 . 8th ed . Washington, DC : US Department of Agriculture ; 2015 . http://health.gov/dietaryguidelines/2015/guidelines/. Accessed October 19, 2017. 3 Purdue-Smithe AC , Whitcomb BW , Szegda KL , et al. . Vitamin D and calcium intake and risk of early menopause . Am J Clin Nutr . 2017 ; 105 ( 6 ): 1493 – 1501 . Google Scholar PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Epidemiology Oxford University Press

RE: “DIETARY PROTEIN INTAKE AND EARLY MENOPAUSE IN THE NURSES’ HEALTH STUDY II”

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Publisher
Oxford University Press
Copyright
© The Author(s) 2018. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
ISSN
0002-9262
eISSN
1476-6256
D.O.I.
10.1093/aje/kwy058
Publisher site
See Article on Publisher Site

Abstract

The recent study by Boutot et al. (1) will be of interest to those working in the field of bone health, as early menopause is a key risk factor for osteoporosis. New knowledge on lifestyle factors that might help prevent the condition is of value to women who may be at risk and to those involved in providing advice. Ceasing smoking and increasing physical activity are clear recommendations that are easy to understand, whereas nutritional factors and the concept of a healthy diet often appear inconsistent and vague by comparison. Current advice by the US Department of Agriculture provides examples of diets that would meet guidelines for healthy nutrient intakes (generally diets low in saturated fats and rich in fruit and vegetables) (2), but there is room for refinement. It is important to understand which nutrients and dietary factors might be the drivers behind any observed relationship with a particular health outcome. It is difficult to undertake dietary intervention studies, as changes in one food group or nutrient can affect others if energy intakes are to remain constant. Epidemiologic studies involving large numbers of women, such as the Nurses’ Health Study (http://nurseshealthstudy.org/), are useful, although any associations observed may prove not to be causal. The report by Boutot et al. (1) suggests that intake of vegetable protein is associated with reduced risk of early menopause. We would add a word of caution in highlighting “vegetable protein” together with a recommendation of servings per day of protein-rich foods, as one might be led to believe that this applies to foods such as nuts and soy protein. The authors found that the foods behind the association were pasta, dark bread, and cold cereal (1); these are usually thought of as carbohydrate-rich foods rather than sources of protein, and they also provide minerals and B vitamins. Could the authors clarify whether “cold cereal” refers to processed breakfast cereals (which are often fortified with vitamins and eaten with milk)? A recent study involving the same population showed that intakes of vitamin D and dairy foods were associated with a reduced risk of early menopause (3). Although there may have been good reasons to explore these dietary factors separately from the protein relationship, these individual analyses can build up a confusing picture of which factors are important. Both analyses corrected for the alternative factors, so we know that they are independent predictors, although in both cases the alternative study was not referenced. We request that Boutot et al. provide the effect sizes and confidence intervals for both factors included in the same model, so that readers are clear about their relative importance. Further, we would ask that they consider the use of data reduction techniques (e.g., principal components analysis) to produce dietary patterns. The results of dietary pattern analysis conducted using this large data set could provide a clear dietary message for reducing the risk of early menopause and could assist policy-makers in producing more focused dietary recommendations in the future. Acknowledgments Conflict of interest: none declared. References 1 Boutot ME , Purdue-Smithe A , Whitcomb BW , et al. . Dietary protein intake and early menopause in the Nurses’ Health Study II . Am J Epidemiol . 2018 ; 187 ( 2 ): 270 – 277 . Google Scholar CrossRef Search ADS PubMed 2 US Department of Health and Human Services; US Department of Agriculture . Dietary Guidelines for Americans 2015–2020 . 8th ed . Washington, DC : US Department of Agriculture ; 2015 . http://health.gov/dietaryguidelines/2015/guidelines/. Accessed October 19, 2017. 3 Purdue-Smithe AC , Whitcomb BW , Szegda KL , et al. . Vitamin D and calcium intake and risk of early menopause . Am J Clin Nutr . 2017 ; 105 ( 6 ): 1493 – 1501 . Google Scholar PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

American Journal of EpidemiologyOxford University Press

Published: Mar 23, 2018

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