Vitamin D intake, month the mammogram was taken and mammographic density in Norwegian women aged 50-69.
BACKGROUND
The role of vitamin D in breast cancer etiology is unclear. There is some, but inconsistent, evidence that vitamin D is associated with both breast cancer risk and mammographic density (MD). We evaluated the associations of MD with month the mammogram was taken, and with vitamin D intake, in a population of women from Norway--a country with limited sunlight exposure for a large part of the year.


METHODS
3114 women aged 50-69, who participated in the Norwegian Breast Cancer Screening Program (NBCSP) in 2004 or 2006/07, completed risk factor and food frequency (FFQ) questionnaires. Dietary and total (dietary plus supplements) vitamin D, calcium and energy intakes were estimated by the FFQ. Month when the mammogram was taken was recorded on the mammogram. Percent MD was assessed using a computer assisted method (Madena, University of Southern California) after digitization of the films. Linear regression models were used to investigate percent MD associations with month the mammogram was taken, and vitamin D and calcium intakes, adjusting for age, body mass index (BMI), study year, estrogen and progestin therapy (EPT), education, parity, calcium intakes and energy intakes.


RESULTS
There was no statistical significant association between the month the mammogram was taken and percent MD. Overall, there was no association between percent MD and quartiles of total or dietary vitamin D intakes, or of calcium intake. However, analysis restricted to women aged <55 years revealed a suggestive inverse association between total vitamin D intake and percent MD (p for trend = 0.03).


CONCLUSIONS
Overall, we found no strong evidence that month the mammogram was taken was associated with percent MD. We found no inverse association between vitamin D intake and percent MD overall, but observed a suggestive inverse association between dietary vitamin D and MD for women less than 55 years old.
University of OsloOslo, Norway.
Merete
M
Ellingjord-Dale
Department of Non-Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
Isabel
I
dos-Santos-Silva
Cancer Registry of Norway, Oslo, Norway.
Tom
T
Grotmol
Norwegian Institute of Public Health, Oslo, Norway.
Amrit Kaur
AK
Sakhi
Cancer Registry of Norway, Oslo, Norway.
Solveig
S
Hofvind
Norwegian Centre for Minority Health Research, Oslo, Norway.
Samera
S
Qureshi
University of OsloOslo, Norway.
Marianne Skov
MS
Markussen
Norwegian Knowledge Centre for the Health Services, Health Economic and Drug Unit, Oslo, Norway.
Elisabeth
E
Couto
Cancer Registry of Norway, Oslo, Norway.
Linda
L
Vos
University of OsloOslo, Norway; Cancer Registry of Norway, Oslo, Norway; University of Southern California, Los Angeles, United States of America.
Giske
G
Ursin
D000368:Aged; D000071060:Breast Density; D001943:Breast Neoplasms / Q000097:blood / Q000000981:diagnostic imaging* / Q000453:epidemiology; D002136:Calcium, Dietary / Q000494:pharmacology; D005260:Female; D005843:Geography; D006801:Humans; D042361:Mammary Glands, Human / Q000002:abnormalities*; D008327:Mammography; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D012307:Risk Factors; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology*
D002136:Calcium, Dietary; D014807:Vitamin D; C104450:25-hydroxyvitamin D