Changes in iron measures over menopause and associations with insulin resistance.
OBJECTIVE
No longitudinal studies have examined how iron measures change over menopause. Our objectives were to examine iron measures in individual women at premenopause and at postmenopause and, secondarily, to determine if any changes contributed to insulin resistance.


METHODS
In a subset of participants (n=70) in a longitudinal study of menopause, we measured ferritin, transferrin, and soluble transferrin receptor (sTfR) once in the premenopause and once in the postmenopause. We also examined associations between menopausal status and change in iron markers after adjustment for age at menopause, race/ethnicity, and waist circumference. In linear regression models, we examined associations between premenopause iron measures and changes in iron markers over menopause with homeostasis model assessment of insulin resistance (HOMA-IR) changes over menopause, before and after adjustment for age at menopause, race/ethnicity, changes in waist circumference, C-reactive protein (CRP), and sex hormone-binding globulin (SHBG) levels.


RESULTS
Women had lower ferritin (p<0.01), higher sTfR:ferritin levels (p<0.01), lower HOMA-IR (p=0.022), and lower glucose (p=0.05) in premenopause compared to postmenopause. After adjustment, lower premenopausal iron levels (sTfR:ferritin levels β=11.0, 95% confidence interval [CI] 0.017-22.0) and larger increases in iron over menopause (changes in sTfR:ferritin β=13.6, 95% CI 0.93-26.3) were associated with larger increases in HOMA-IR.


CONCLUSIONS
From premenopause to postmenopause, women on average have increases in measures of iron stores. Women who had the greatest changes in iron over menopause (lower measures of premenopausal iron and greater increases in iron measures over the menopause) had the strongest associations between changes in iron and changes in insulin resistance.
Department of Medicine, Obstetrics & Gynecology, University of Michigan, Ann Arbor, Michigan 48109-5429, USA. cathkim@umich.edu
Catherine
C
Kim
Bin
B
Nan
Shengchun
S
Kong
Siobhan
S
Harlow
D000328:Adult; D015415:Biomarkers; D001786:Blood Glucose / Q000378:metabolism; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D005293:Ferritins / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D007501:Iron / Q000378:metabolism*; D008137:Longitudinal Studies; D008875:Middle Aged; D017698:Postmenopause / Q000097:blood* / Q000208:ethnology; D017697:Premenopause / Q000097:blood* / Q000208:ethnology; D011990:Receptors, Transferrin / Q000378:metabolism; D012738:Sex Hormone-Binding Globulin / Q000502:physiology; D014168:Transferrin / Q000378:metabolism; D055105:Waist Circumference / Q000502:physiology
D015415:Biomarkers; D001786:Blood Glucose; D011990:Receptors, Transferrin; D012738:Sex Hormone-Binding Globulin; D014168:Transferrin; D002097:C-Reactive Protein; D005293:Ferritins; D007501:Iron