Calcium intake levels of more than 800 mg/day may be unnecessary for maintaining calcium metabolism if vitamin D status is adequate, according to a study in the November 9 issue of JAMA: The Journal of the American Medical Association.
The importance of adequate vitamin D status for optimum bone health has received increased recognition in recent years, with higher recommended intake levels being proposed by some investigators, according to background information in the article. The ideal intake is not known, and different criteria have been proposed for estimating population requirements. Serum 25-hydroxyvitamin D has been the generally accepted indicator of vitamin D status, but no universal consensus has been reached regarding which serum values constitute sufficiency. An inverse relationship between serum 25-hydroxyvitamin D and serum parathyroid hormone (PTH) is well established. Parathyroid hormone is a major hormone maintaining normal serum concentrations of calcium and phosphate and is itself regulated through levels of calcitriol and serum calcium. An insufficiency of vitamin D or calcium is generally associated with an increase in PTH.
Laufey Steingrimsdottir, Ph.D., of Landspitali-University Hospital, Reykjavik, Iceland, and colleagues conducted a study to determine the importance of high calcium intake and serum 25-hydroxyvitamin D for calcium homeostasis (metabolic equilibrium) in healthy adults, as determined by serum intact PTH.
The study included 2,310 healthy Icelandic adults who were divided equally into 3 age groups (30-45 years, 50-65 years, or 70-85 years) and recruited from February 2001 to January 2003. They were administered a semi-quantitative food frequency questionnaire, which assessed vitamin D and calcium intake. Participants were further divided into groups according to calcium intake (less than 800 mg/d, 800-1200 mg/d, and greater than1200 mg/d) and serum 25-hydroxyvitamin D level (less than 10 ng/mL, 10-18 ng/mL, and greater than 18 ng/mL). A total of 944 participants completed the dietary questionnaire.
The researchers found that after adjusting for relevant factors, serum intact PTH was lowest in the group with a serum 25-hydroxyvitamin D level of more than 18 ng/mL but highest in the group with a serum 25-hydroxyvitamin D level of less than 10 ng/mL. At the low serum 25-hydroxyvitamin D level (less than 10 ng/mL), calcium intake of less than 800 mg/d vs. more than 1200 mg/d was significantly associated with higher serum PTH; and at a calcium intake of more than 1200 mg/d, there was a significant difference between the lowest and highest vitamin D groups.