Update on calcium and vitamin D
There is a recent issue of Endocrinology and Metabolism Clinics of North America dedicated to the subject of osteoporosis. The editor is John P. Bilezikian, MD, and it is Volume 32, Number 1, March 2003. These journals are directed to health care providers, but often have a wealth of knowledge for the layman, too. Here are the chapter topics covered in the book: Epidemiology Worldwide, Pathogenesis of Osteoporosis, The Structural and Biomechanical Basis of the Gain and Loss of Bone Strength in Women and Men, Establishment of Peak Bone Mass, Genetic Determinants of Susceptibility to Osteoporosis, Biochemical Markers of Bone Remodeling, Secondary Osteoporosis, Glucocorticoid-Induced Osteoporosis, Bone Mineral Density--Clinical Use and Application, Calcium and Vitamin D, The Role of Estrogens in Men and Androgens in Women, Selective Estrogen Receptors Modulators in the Prevention and Treatment of Postmenopausal Osteoporosis, Phytoestrogens--Mechanism of Action and Effect on Bone Markers and Bone Mineral Density, Bisphosphonates, Calcitonin, New Anabolic Therapies in Osteoporosis. Since calcium and vitamin D are so essential in the treatment of osteoporosis, I want to review that chapter now. I may do updates later on other chapters if the information is important enough.
General information. The use of calcium and vitamin D is discussed on pages 181-94 by Heaney RP and Weaver CM. PMID: 12699298. Much of the discussion is quite complex, but I'll try to just summarize the details that seem pertinent for people with osteoporosis. Please read the article yourself if you want to get the complete picture. What the authors point out is that there has to be sufficient intake of calcium daily to offset daily losses of calcium that occur through the skin, the urine, and the feces. Otherwise, calcium will be removed from the bones to support other bodily needs of the element. They use the chemical terminology of mmol (millimoles) to describe the amount of calcium needed, used, lost, etc. We are more used to hearing about grams or milligrams. To convert these two measurements, figure that 31 mmol of calcium is about equal to 1240 mg. Or, 1 mmol equals 40 mg calcium. The importance of vitamin D is that it allows for the active transport of calcium across the gut, the only way to increase absorption of calcium to meet increased needs. Renal calcium conservation is weak and skin losses are unregulated. Also, net calcium absorption is only about 10% of a 25 mmol intake, with half of this going to replace skin and renal losses under normal conditions. Thus, more than 25 mmol/d of calcium may be required just to maintain the status quo. If someone exercises regularly and sweats a lot, enough calcium can be lost through sweat so that there is inadequate calcium remaining to preserve bone. Also, remember that a very high fiber diet--probably the healthiest way to eat--can also reduced absorption of calcium from the gut. So, if you eat this way, consider taking some of your calcium mid-meals with a low fiber snack, at bed time, and/or take more calcium that is recommended since you aren't absorbing all that you take.
Vitamin D. [NOTE: To convert the various vitamin D lab results remember 1 ng/mL = 2.5 nmol/L and you must examine your lab slip to see exactly what measurement they report the results with. A reading of 40 ng/mL is well in the normal range. One of 40 nmol/L is below the normal range considerably]. It was traditionally thought that 400 IU of vitamin D taken orally per day was adequate. But, this was based upon the ability to prevent rickets, not to maintain ideal bone density. Actually, there is evidence that daily vitamin D inputs normally range from 3000 to 5000 IU, both from sunlight and oral sources. And, the problem can arise in older individuals who have reduced sun exposure and whose bodies no longer convert the inactive vitamin D to the active form when hit by sunlight. This level of daily intake historically was expected to produce "normal" serum levels of vitamin D with a lower limit of 40 to 50 nmol/L. The authors note that current evidence points to 80 nmol/L as being a more realistic lower level. In order to get this level of serum vitamin D, individuals (particularly older people not exposed to sun) need an oral intake of at least 1000 IU/d of vitamin D. [NOTE: This amount is somewhat greater than I've seen heretofore. Generally 800 IU has been described as the right intake of vitamin D, so this may mean that some of you will need to increase your daily dose of vitamin D]. [NOTE: I keep track of all my lab results, so I checked to see what my vitamin D results were when last taken several years ago. The test showed 33 and I didn't record if it was ng/mL or nmol/L, so I need to do more research to see if I'm in the normal range, or well below it. I recommend you check your lab results to see if your vitamin D levels have been tested and whether those results are normal or not. If needed, then increase your daily intake of vitamin D and have the test repeated to verify you have been able to increase serum levels to the normal range].
Prevention. It appears that adolescents are not getting adequate calcium intake to develop peak bone mass, which is important to help prevent osteoporosis or osteopenia. Studies have shown that 9 to 13 year old girls in the U.S. averaged 23 mmol/d of calcium intake. However, to attain mean maximal calcium retention they needed 32.5 mmol/d. At that extra dose, 4% of skeletal mass could be gained. What is really interesting is that much bone accrual occurs during a two-year period in both boys and girls: Peak accrual for girls at age 12.5 and for boys at 14 years. Unfortunately, this isn't an age when children are always susceptible to good dietary advice. Here's an interesting study by Peacock and others, PMID: 10999778 that sheds light on the importance of the dose of calcium and its relationship to vitamin D supplementation. What this study showed was that adding vitamin D for people with severe calcium deficiency isn't helpful. Actually, getting calcium intake to the required 34 mmol/d level was more effective at preventing bone loss. Thus, it appears that the ideal is to have proper calcium intake daily--either through diet or supplements--and to maintain a serum vitamin D level of at least 80 nmol/L. To expect one to work without the other being present is unrealistic. Recommended daily calcium intake for people older than 50 is 37.5 mmol, or 1500 mg/day. Note that the best way to get this is in smaller amounts (if from the diet) or in about 250 mg supplements. Absorption is better in smaller doses. Here is a quote from a recent newsletter from another Dr. Heaney article: "Calcium absorption efficiency varies inversely as the logarithm of the size of the load. Accordingly, if rather than taking a 1000-mg dose of calcium, it was divided into two doses of 500 mg each, 30% additional calcium would be absorbed. Or, if this 1000-mg dose was divided into four doses of 250 mg each, then 60% more calcium would be absorbed."
Therapeutic support. All the clinical trials of the bisphosphonates for treating osteoporosis have used supplemental calcium and some have also added vitamin D. Thus, there is no control group to validate the importance of the calcium/vitamin D to increase BMD after taking the bisphosphonate. There is evidence from studies on women taking hormone replacement therapy (HRT) and also taking calcium supplements that the calcium is very important, often doubling the improvement in BMD compared to just using HRT alone. And, in clinical trials of teriparatide (Forteo), one study whose participants took 50% more calcium than those in a comparable study found BMD increased by about one-third relative to the lower calcium group. Thus, the evidence points to the importance of adequate calcium and vitamin D intake while taking any of the FDA-approved therapies for osteoporosis.
Sources. The best source of calcium is foods, dairy products or fortified foods that have established bioavailability of their added calcium. Food has other elements that are needed for bone health such as protein, potassium, magnesium and phosphorus. Milk and yogurt have the best and most economical source of calcium in a single package. If supplements are needed, manufacturers' claims notwithstanding, all chemical salts of calcium are about equally well absorbed. The authors recommend choosing a supplement that has established and published absorbability since some formulations do have reduced absorbability. The choice for vitamin D is not so obvious. Although many calcium products also have vitamin D, it is usually in less than ideal amounts. It can be hard to find vitamin D-only preparations, although there is a prescription form of vitamin D2 in a 50,000 IU formulation if you can't reached desired serum levels of vitamin D otherwise. But, a combination of a calcium/vitamin D supplement, plus a daily multi-vitamin with vitamin D and fortified milk or cereal might be the best choice. To reach ideal levels, individuals probably need some time in the sun, too. General Nutrition Centers has vitamin D supplements (cholecalciferol) in 700 IU formulation and there may be other pharmacies, drug stores, etc., that carry such products. If a person takes 700 IU/day and just drinks milk with vitamin D or takes a multivitamin with vitamin D, they would surely reach the 1000 IU/day recommendation of the authors.
Summary. Based upon the latest research it appears that we should be taking at least 1500 mg/day of calcium in small increments throughout the day. Ideally this should be calcium-containing foods such as dairy products and fortified foods. If you can't get that much calcium via foods, then take a supplement, preferably one that also has vitamin D and that has published absorbability. The minimum serum level of vitamin D should be 80 nmol/L. To attain this level 1000 IU/day of vitamin D are needed. Thus it is suggested people take a vitamin that contains vitamin D, calcium/vitamin D supplements, and milk that has vitamin D. Get some sunshine if possible since that is the best source of vitamin D.