Most people know that adequate calcium in the diet is essential for strong bones and teeth. There has also been a lot of information written regarding the effect of calcium on the development or prevention of osteoporosis and bone fractures.
Were you also aware that vitamin D may be equally important in the prevention of osteoporosis and bone fractures so closely linked to the aging process? Well, new research published in the Journal of Clinical Endocrinology and Metabolism indicates that vitamin D may not be all that is required for adequate bone health.
Researchers evaluated 159 postmenopausal women over a six-month period and randomly assigned them to one of four groups. The groups were provided with either double placebo treatment pills; 1,200 mg of calcium plus placebo; or 4,000 IU of vitamin D plus placebo, calcium, and vitamin D. At the beginning of the study and again at three and six months, the study participants provided urine and blood samples after a calcium load to measure the rate of bone turnover.
The results of the study clearly indicated that the participants taking supplementation with calcium or vitamin D experienced lowered levels of parathyroid hormone; however, the participants who took the 1,200 mg of calcium supplements also experienced reduced markers of bone turnover, whereas the participants who took 4,000 IU of vitamin D did not.
According to the author of the study, Dr. J. Aloia, vitamin D and calcium interact to suppress bone turnover by decreasing parathyroid hormone levels. “This can be beneficial in women who are vitamin D deficient. In women who already are receiving the recommended daily allowance of vitamin D, however, the study found there was no advantage to adding a vitamin D supplement.”
He noted that “these findings suggest that vitamin D supplements over the recommended dietary allowance…do not protect bone health, whereas calcium supplements do have an effect. Women do need to be cautious about the possibility of vascular side effects from too much calcium and should consult their physicians about whether their diet is adequate or whether they should take supplements at all.”
Although this is an interesting study, there are a number of issues with it which do not support Dr. Aloia’s view. There were some issues regarding the measurement of vitamin status, parathyroid hormone, and a total lack of a relationship that evaluates the dose of a nutrient and the response upon a physiological variable, in this case, bone turnover and parathyroid levels. The subjects were also healthy without any evidence of osteoporosis and there was no clinical relationships made regarding fracture prevention.
In my opinion, vitamin D is a nutrient which is much more likely to be deficient in the human diet compared to calcium and although some people do not get enough calcium in their diets, vitamin D status is much more of a problem for most people as an adequate supply is impossible to get from dietary sources alone.
Although vitamin D does decrease parathyroid hormonal levels which decreases bone reabsorption, it also allows an adequate amount of elemental calcium to be absorbed in the gut and prevents the excretion of calcium in the kidney. Vitamin D increases blood levels of calcium and this is the mechanism by which calcium slows down bone turnover through its influence upon parathyroid secretion.
Post-menopausal women need an average amount of 1,200-1,500 mg of elemental calcium per day and at least 1,000-2,000 IU of vitamin D to maintain and protect optimum bone integrity by slowing down the process of bone turnover.
Source(s) for Today’s Article:
Barclay, L.,“Vitamin D Alone Ineffective for Postmenopausal Osteoporosis,” Medscapewebsite, Sept. 24, 2013;http://www.medscape.com/viewarticle/811548
Aloia, J., etal.,“Calcium and Vitamin D Supplementation in Postmenopausal Women,”The Journal of Clinical Endocrinology & Metabolism.September 24, 2013.