Calcium, Vitamin D, and Osteoporosis
About 10 million Americans already have osteoporosis, and 34 million are at risk.1 Contrary to popular belief however, low intake of calcium is not the primary cause of osteoporosis. While Americans have the highest calcium intake in the world, we also have one of the highest hip fracture rates in the world.2 The standard American diet causes much of the consumed calcium to be lost in the urine. Excess salt, caffeine, sugar, and animal products leach calcium out of bones and promote urinary calcium loss.3 The Nurses' Health Study followed 72,337 women for over 18 years and found that dairy intake did not reduce the risk of osteoporosis-related hip fractures.4
In contrast, vegetables, beans, fruits, nuts, and seeds are rich sources of calcium and other important minerals, and do not promote the urinary excretion of calcium. A three cup serving of raw, chopped greens – like kale, bok choy, or collards - provides the same amount of calcium (or more) as one cup of whole milk. Only 32% of the calcium in the cup of cow’s milk can be absorbed by the human body compared to about 50% for many green vegetables.5
Calcium isn't the only important nutrient for bone health
It’s also important to keep in mind that the effect of nutrition on bone health is more complex than just getting adequate calcium. For example, vitamin K also supports bone health; vitamin K1 is abundant in leafy greens, and K2 is an important nutrient to supplement.6 Of course,
vitamin D also plays a critical role in regulating bone health. Vitamin D promotes the absorption of calcium in the intestine as well as the activity of bone building cells. Medical studies show vitamin D is more effective than calcium for treating osteoporosis.7 The most natural way to obtain vitamin D is through sun exposure, but because of indoor jobs, our climate, and skin cancer risk it is virtually impossible to achieve optimal levels of Vitamin D from sunshine alone. Vitamin D supplementation is necessary for most people.
How much calcium and Vitamin D are necessary to protect against osteoporosis?
Most Americans take inadequate amounts of Vitamin D and excessive amounts of calcium. Approximately 50% of Americans are deficient in Vitamin D.8 For optimal bone protection, I advise having a blood 25(OH)D test, and then supplementing accordingly to keep Vitamin D levels in the range of 30-45 ng/ml.9,10 If you have not had yet your blood tested, 2000 IU is a reasonable daily dose to start.
Too much calcium may interfere with Vitamin D's effects on bone health.
Calcium should not be taken in excess, and I recommend limiting supplemental calcium to 400-600 mg. Most of your calcium should be derived from plant foods, not supplements. A recent meta-analysis of many studies has shown that low dose (less than 1000 mg) calcium supplementation combined with vitamin D was effective at preventing osteoporosis-related fractures whereas high dose (1000 mg or more) calcium supplementation was not.11,12,13 Overdosing on calcium actually deactivates the Vitamin D and can weaken bones.
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8University of California - Riverside (2010, July 19). More than half the world's population gets insufficient vitamin D, says biochemist. ScienceDaily. Retrieved February 17, 2011, from http://www.sciencedaily.com¬ /releases/2010/07/100715172042.htm
9Bischoff-Ferrari, H.A., Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes. Adv Exp Med Biol, 2008. 624: p. 55-71.
10Bischoff-Ferrari HA, Giovannucci E, Willett WC, et al., Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr, 2006. 84(1): p. 18-28.
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13Bischoff-Ferrari HA, Orav EJ, Willett, WC, et al., A Higher Dose of Vitamin D is Required for Hip and Non-vertebral Fracture Prevention: A Pooled Participant-based Meta-analysis of 11 Double-blind RCTs, in The American Society for Bone and Mineral Research 2010 Annual Meeting2010: Toronto, Ontario, Canada.