Vanessa R. Yingling, Ph.D. FACSM co-chairs the American College of Sports Medicine’s Bone and Osteoporosis Network Exchange, facilitating multi-disciplinary approaches to the study of bone health. An assistant professor of Kinesiology at California State University, she is also an author of numerous studies on bone health and metabolism. Jennifer Sherwood, Ph.D., CSCS, an exercise physiologist with specialties in biochemistry, nutrition, and human metabolism, is an assistant professor of Kinesiology at California State University, East Bay; a professional consultant for California’s Physical Education-Health Project, advising physical and health education teachers on comprehensive content related to physical fitness, nutrition and health; and the faculty director of Get Fit! Stay Fit!, the fitness and wellness program for CSU faculty and staff.
HHN: Can you help sort out whether or not calcium supplements do prevent osteoporosis-related fractures? Different studies have come to opposite conclusions. For example, a 2010 study published in the British Medical Journal, which analyzed 68,500 patients from 7 American and European trials, found that participants supplementing with both calcium and vitamin D had a significantly decreased risk of fractures in comparison to those who solely received vitamin D supplements. However, a July 2015 review, published in the Journal of Internal Medicine, concluded: "Most studies show little evidence of a relationship between calcium intake and bone density, or the rate of bone loss… Five recent large studies have failed to demonstrate fracture prevention." How do you make sense of these significant discrepancies?
VY/JS: Let’s dig into the main clinical outcome measure: fracture. These and other studies assume that calcium balance and bone density are strongly related to fracture risk. [pullquote-right] "Fewer than 50% of fractures are attributed to osteoporosis!" [/pullquote-right] Now, while it’s true that low bone mineral density is related to increased fracture incidence, many fractures also occur in people who don’t have osteoporosis based on the most commonly used bone- density definition. In fact, fewer than 50% of fractures are attributed to osteoporosis! In one study of nearly 10,000 women aged 65+, published in the official journal of the American Society for Bone and Mineral Research, the proportion of fractures attributable to osteoporosis ranged from under 10% to 44%!
Many other factors impact upon fracture risk, including poor posture reflexes, high incidence of falls, low body mass index (which may exacerbate impact trauma), prior history of fractures, [pullquote-right] "The World Health Organization’s fracture risk assessment tool, FRAX FRC, doesn’t even ask about calcium consumption!" [/pullquote-right] a parental history of hip fracture (know your family medical history, as osteoporosis has a genetic component), rheumatoid arthritis, smoking, and alcohol intake of 3 or more daily servings). (See this study assessing fracture probability, this study relating high alcohol intake to osteoporotic and hip fracture risk, and this study associating current smoking with fracture risk for more information.)
Notably, both FRAX FRC (the World Health Organization’s fracture risk assessment tool) and FORE FRC (Foundation for Osteoporosis Research and Education Fracture Risk Calculator) don’t even ask about calcium consumption!
All of this, however, does not mean that calcium is unimportant in osteoporosis prevention. Extremely low calcium levels—under 400 mg per day—appear connected to a large rate of bone loss. Animal trials, such as this classic study, do link osteoporosis to low calcium intake.
HHN: While low calcium levels are linked to osteoporosis in animals, how do we know this finding is applicable to humans?
VY/JS: We don’t, exactly. To establish this link and determine a dose-dependent effect in humans, scientists would have to restrict calcium from the diets of human volunteers for perhaps over a year before bone density measures might detect a significant reduction in bone mass—a potentially harmful and unethical type of study.
HHN: Is there, then, any ideal calcium target, or at least a range, to minimize osteoporosis and fracture risk?
VY/JS: The truth is, optimal calcium intake levels remain unresolved and Recommended Daily Allowance (RDA) levels vary considerably by country. Compare these:
- United States / National Institute of Health RDA: 1,000 — 1,200 mg
(women 19 — 50: 1,000 mg; women 51+: 1,200 mg; men 19 — 70: 1000 mg; adults 70+: 1,200 mg)
- Nordic Cooperative (Norway, Sweden, Denmark, Finland, etc.): 800 mg (all adults)
- United Kingdom: 700 mg (all adults)
- Germany: 1,000 mg (all adults)
- Canada: 1,000 — 1200 mg (men 19−70 1,000 mg; women 19−50 1,000 mg, women 51−70 1,200 mg)
Moreover, as this American Journal of Clinical Nutrition article notes, many world populations have lower calcium diets than ours and do not have excessive fracture rates "as would be expected if calcium requirements were far above their usual intake."
HHN: Why are there such marked differences in countries' recommended calcium intake levels?
VY/JS: Each nation’s calcium recommendation is primarily based on what’s known as calcium balance studies. Basically, calcium requirements [pullquote-right] "The Recommended Daily Allowance for calcium varies considerably by country." [/pullquote-right] for adults throughout the word are defined as the amount of dietary calcium required to yield an equilibrium between intake and excretion. In other words, the target is an intake level whereby the body doesn’t lose calcium—a zero calcium balance.
The challenge with this methodology, however, is that calcium excretion depends on many factors beyond calcium intake, among them [pullquote-right] "Extremely low calcium levels—under 400 mg per day—appear connected to a large rate of bone loss." [/pullquote-right] body weight, physical activity level, dietary protein intake and quality, and smoking and alcohol consumption. And because these factors vary widely between countries, they affect the results of calcium balance studies and, thereby, each nation’s calcium recommendations.
Contributing to the confusion, there may be a mismatch between an individual’s calcium needs and his/her country’s calcium intake recommendations as a result of individual absorption differences as well as nutrient and estrogen/testosterone variations, among other factors.
HHN: Given all these nuances, it sounds like calcium’s importance in osteoporosis prevention might be overemphasized these days.
VY/JS: Yes, recommendations based solely on daily calcium consumption are woefully inadequate. While it is vital to get sufficient calcium, when it comes to osteoporosis prevention, ingesting high levels of calcium is unlikely to counteract other lifestyle choices such as physical inactivity, smoking, alcohol consumption, and a poor overall diet.
Instead, osteoporosis prevention recommendations should focus on a healthy and varied diet with overall nutrient sufficiency—especially Vitamin D—as well as physical activity.
Vitamin D & Osteoporosis Prevention
HHN: Why is Vitamin D particularly important in osteoporosis prevention?
VY/JS: Vitamin D is important for bone mineralization. Lack of vitamin D delays bone mineralization, and ultimately causes plasma calcium levels to fall. Getting vitamin D, meanwhile, has been shown to facilitate calcium absorption.
In the U.S. the Vitamin D RDA is 600 — 800 IU (adults 19 — 70: 600 IU; adults 70+: 800 IU).
When Supplementing Isn’t Smart
HHN: Should readers take calcium or Vitamin D supplements to reach these daily values?
VY/JS: The best approach is to get your nutrients directly from your diet. This will most likely ensure sufficient intakes of other nutrients important to overall health, including bone health (e.g., vitamins C, K, and folate, to name a few), and minimize your risk of medical complications.
Calcium supplementation has been associated with several negative consequences. For example:
One study, published in JAMA Internal Medicine, analyzed 388,000 men and women aged 50- 71 and found a significant association [pullquote-right] "One large study found a significant association between calcium supplementation and men’s risk of death from heart disease." [/pullquote-right] between calcium supplementation and men’s risk of death from heart disease (women were not affected). We’re not sure why calcium supplements and cardiovascular disease appear linked. Possibly, the calcium is being deposited into arterial walls, exacerbating the process of arteriosclerosis (hardening of the arteries).
Some studies also indicate that calcium supplementation raises a woman’s risk of getting kidney stones. A very recent study of 2000 patients, presented at the American Society of Nephrology’s November 2015 conference [pullquote-right] "People are supplementing to prevent one disease, while potentially contributing to another." [/pullquote-right] (and not yet subject to the rigors of peer review), found that calcium supplements, compared to calcium-rich diets, increased the risk of kidney stone recurrence and sped the rate of kidney stone growth. And a 2014 Women’s Health Initiative study reported that eating more fiber, fruits, and vegetables (some of which are rich in calcium) is associated with reduced kidney stone risk.
Furthermore, calcium supplements, particularly the calcium carbonate form, increase the risk of gastrointestinal complications, such as bloating, gas, flatulence, constipation, and/or cramping, which can be serious enough to send you to the emergency room
Lastly, multiple drug-nutrient interactions have been associated with calcium supplements, so people should consult their pharmacist before taking calcium pills.
Overall, the risks of calcium supplementation seem to outweigh the benefits. In effect, people are supplementing to prevent one disease while potentially contributing to another. Moreover, aiming to get RDA requirements met through pills can misdirect us from following a varied, fiber and produce-rich diet—a diet that is vital not only for bone but for our general health.
Still, individuals who routinely fail to meet the calcium RDA through diet should consider supplementing with both calcium and vitamin D.
HHN: If getting calcium through diet is best, what are the optimal sources?
VY/JS: The most plentiful calcium sources include cheese, whey, and calcium-fortified foods, according to the USDA’s ranked list of calcium-rich foods. Here is the NIH’s table of high-calcium foods. For vegans, blackstrap molasses, cooked collard and turnip greens, sesame seeds, calcium-fortified milk alternatives, and calcium sulfate-processed tofu are among the most calcium-rich non-dairy options.
Look at nutrition labels. Every day, choose foods that are high in calcium, including some that provide 20% DV (daily value). And, as part of a healthy diet, keep intake of saturated fat, trans fat, and cholesterol as low as possible. Choose low fat or no fat options when available.
HHN: I’ve heard it said that if you get calcium from dairy sources, it should only be from fermented dairy, such as yogurt or kefir, because the fermentation process increases absorption. Is that true?
VY/JS: Not much evidence exists to support the assertion that fermented dairy products increase calcium absorption or improve bone density in humans. One short-term, randomized, double-blind, crossover study in just 20 women aged 50−78 yrs. did find that milk fermented with Lactobacillus helveticus increased serum calcium compared to unfermented milk, during a short-term (8-hours post-ingestion) period. But to date, this has been the only study of human beings. Most studies with positive results have been performed in rodents, so more clinical work is needed to confirm the results hold true in humans.
HHN: Some of the calcium-rich foods noted above are fortified foods. How is getting calcium from fortified foods different from and/or better than taking a calcium supplement?
VY/JS: Food that naturally contains calcium remains your best calcium option. Nonetheless, for many people, such as vegans [pullquote-right] "The bioavailability of calcium in fortified foods varies considerably." [/pullquote-right] and those with dairy allergies, fortified foods represent an alternative, convenient way to increase calcium intake. Unfortunately, the bioavailability of calcium in fortified foods varies considerably, and this information is not available on food labels.
Vitamin D-Rich Foods
HHN: What common foods contain Vitamin D?
VY/JS: Few foods are naturally rich in vitamin D. The National Institute of Health identifies "fatty fish such as salmon, tuna, and mackerel [as] among the best sources. Beef liver, cheese, egg yolks, and mushrooms provide small amounts."
According to USDA analyses, milk, yogurt, and anchovies are other good sources.
Foods often fortified with vitamin D include milk, butter, orange juice, breakfast cereals, and cheese.
In addition, sunlight converts 7-dehydrocholesterol in our skin to pre-vitamin D3 The pre-vitamin is then converted, by way of the liver and the kidneys, to calcitriol, the biologically active vitamin D. Although sun exposure is important for vitamin D [pullquote-right] "Fatty fish such as salmon, tuna, and mackerel are among the best sources of vitamin D." [/pullquote-right] synthesis, it’s also important for us to limit skin exposure to the sun to minimize melanoma risk. Unfortunately, the sun exposure time to meet vitamin D recommendations is difficult to predict because sunlight-associated vitamin D synthesis depends on many factors, including the amount of skin exposed, use of sunscreen, age, skin pigmentation, latitude, time of day, and season.
Getting Enough Cal/D?
HHN: How can people easily find out if they’re meeting daily calcium/ vitamin D values?
VY/JS: The American Bone Health’s Calcium Rule of 300 is possibly the easiest way to assess calcium intake. Since a general rule of thumb is that most dairy products and calcium-rich foods provide 300 mg of calcium per serving, determine the number of servings you get each day and multiply by 300. Add 300 to your sum if you eat a well-balanced diet. The total is your calcium intake from diet.
Other ways to track calcium/vitamin D include:
https://cronometer.com, which shows, free of charge, how close you have come to meeting your U.S. daily values for protein, vitamins, minerals, and more.
MyFitnessPal, which can also track calcium
HHN: If, at the end of your day, you haven’t reached your calcium and vitamin D values, is it a good idea to supplement? Is "supplement as needed" a good preventive nutritional approach?
VY/JS: Yes, but only supplement with the approximate amount of milligrams you need to reach the daily allowance.
Generally, people seem to believe that more is better, but as we’ve discussed, it’s certainly not true when it comes to calcium and vitamin D. [pullquote-right] "For healthy adults, total calcium/day should remain below 2,000 mgs and vitamin D/day below 4000 IUs." [/pullquote-right] Calcium from food and supplements should not exceed the current RDA. The Institute of Medicine report on calcium/vitamin D states that there are no additional health benefits associated with calcium intakes above the RDA, and advises that for healthy adults, total calcium/day should remain below 2,000 mgs and total vitamin D/day below 4,000 IUs to avoid possible adverse effects.
Selecting the Right Supplements
HHN: If calcium/vitamin D supplements are still needed, what are the most effective kinds for osteoporosis prevention?
VY/JS: The most common forms of calcium are calcium carbonate and calcium citrate. Calcium carbonate is most cost effective, [pullquote-right] "Look for a supplement with an NSF or USP mark on the bottle." [/pullquote-right] but should be taken with a meal for optimal absorption. Basically, calcium carbonate creates a more alkaline environment in the gastrointestinal tract, but calcium absorption depends upon an acidic gastric environment. Since food stimulates gastric acid release, it will help to increase calcium absorption.
Calcium citrate is usually recommended for older adults as well as individuals with inflammatory bowel disease or other absorption disorders. It can be taken without food. However, it contains less calcium per dose, requiring more doses. Calcium lactate and gluconate are less concentrated forms and therefore not as practical as oral supplements.
Look for a supplement with an NSF (NSF International) or USP (US Pharmacopeial Convention) mark on the bottle, which indicates that an independent, third-party organization has certified that the product contents match the label and/or that the manufacturing process meets quality standards.
Start by reading the label for the amount of "elemental calcium" per pill. Elemental calcium is the actual amount [pullquote-right] "Look for the amount of 'elemental calcium'—the amount that will be available to your body." [/pullquote-right] of calcium in the supplement that will be made available to your body. Then, based upon your dietary calcium consumption, determine how many pills you’ll need to get your daily dose.
Note that our bodies are only able to absorb up to 500 mgs of calcium at a time. If more is needed, supplement in multiple doses throughout the day.
As we’ve discussed, if you take a calcium pill, be sure to also supplement with vitamin D. Of the two commonly available forms, D2 and D3, studies suggest that D3 is more potent.
HHN: Is there anything else you’d like to say to readers about calcium, vitamin D, and osteoporosis prevention?
VY/JS: Bottom line: Try to meet your calcium and Vitamin D values with foods in a nutritious diet. This will likely ensure sufficient intakes of other nutrients [pullquote-right] "Bottom line: Try to meet your calcium and Vitamin D values with foods in a nutritious diet." [/pullquote-right] important to overall health, including bone health (e.g. vitamins C, K and folate), and minimize your risk of medical complications. Supplement with both nutrients only if necessary to reach—and never to exceed— your daily values, and before you do, speak to your pharmacist about potential interactions between the supplements and medications you may be taking.
Most of all, remember this: Exercise is just as important, and likely [pullquote-right] "Exercise is likely even more important in preventing osteoporosis and related fractures." [/pullquote-right] even more important, in preventing osteoporosis and osteoporosis-related fractures. To learn which kinds of exercises are most likely to reduce your risk, stay tuned for Part II in this series.by