The results of a new study were supposed to resolve a persistent bone-protection conundrum.
Do calcium and vitamin D help post-menopausal women prevent bone breaks, or not?
Unfortunately, the mixed results of this large, placebo-controlled trial reflected its weaknesses, and were therefore inconclusive despite some positive findings.
And news headlines tended to distort the study's findings by overplaying the negative aspects, underplaying the positive, and overlooking the weaknesses that make it much less than conclusive.
Results were more positive than media reports suggest
Based on the majority of news headlines, you’d think the study found no benefit from calcium and vitamin D.
But in fact, the participants who took the supplements most consistently enjoyed a significant, 29 percent reduction in their risk of bone fractures.
The new study — part of the Women's Health Initiative (WHI) project — was designed to test the ability of supplemental calcium and vitamin D to protect older women against bone fractures.
And, as with the recent, regrettably flawed evidence review regarding the ability of marine omega-3s to inhibit cancer, both the WHI fracture-prevention study and media mischaracterizations of its findings have provoked an outcry from many expert observers.
Some of these critics expressed their dismay in the letters to the New York Times excerpted below (see "Experts critique conclusions and media characterizations”).
Let’s take a closer look at the design and findings of the new WHI study, starting with the vitamin D aspect.
What the new study actually showed
The new, headline-making study was a large, seven-year investigation of the fracture-preventing effects of supplemental calcium and vitamin D in healthy women over 50. The $18 million study involved 36,282 normal, healthy women aged 50 to 79.
Study participants were randomly assigned to take 1,000 milligrams of calcium and 400 international units of vitamin D a day, or placebo pills, and were followed for seven years. Researchers looked for effects on bone density, fractures and colorectal cancer.
The supplement regimen produced an average one-percent increase in bone density at the hip across all 36,282 women.
However, many participants were "non-compliant”, and did not take the supplements as regularly as required to determine the effects of the supplements with confidence.
The good news is that among the sub-group of women who took at least 80 percent of their pills (termed "compliant”), hip fractures were reduced by 29 percent compared with women who took placebo pills.
We should note that these "compliant” participants may be different from the non-compliant participants in ways that could affect bone strength (i.e., higher protein and magnesium intake, more weight-bearing exercise).
Nonetheless, study director Elizabeth G. Nabel, M.D.—who is also the new Director of the National Heart, Lung, and Blood Institute—told media outlets that the positive results seen in the most compliant subgroup, and the one percent increase in hip bone density seen in the entire group, suggest that taking calcium and vitamin D have value.
As Dr. Nabel said, "Based on all the results, women—particularly those over 60—should consider taking calcium and vitamin D for bone health."
Vitamin D dose called too low
As one of the critiques published by the New York Times pointed out, the dose of vitamin D used—400 IU per day—is considered inadequate by leading researchers in the field. Consequently, the new WHI study tells us little about the ability of dietary vitamin D to protect against fractures.
In fact, the results of several recent studies suggest that vitamin D is more critical than calcium for bone strength. For more information on this key point see "Fractures follow falls: can vitamin D help?” (below), "Women Need to Bone Up on Vitamin D" and "Vitamin D Called More Critical for Bones than High-Dose Calcium."
The experts’ recommended solution to America’s epidemic shortage of vitamin D is to spend at least a half-hour in the sun every day (15 minutes if you have fair skin)—without sunscreen—take 1,000 IU of vitamin D in supplemental form, and/or eat foods rich in vitamin D regularly. (Note: the lowest intake level at which adverse effects might occur is 2,000 IUs, which means that it’s very hard to overdose on vitamin D.)
Vital Choice fish fit the last part of this prescription perfectly. An independent lab measured the amount of vitamin D in 3.5 ounce servings of our fish, and the tests ranked sockeye salmon first (687 IU), followed by albacore tuna (544 IU), silver salmon (430 IU), king salmon (236 IU), sardines (222 IU), halibut and sablefish. (For the full results, click here.)
This means that a single 3.5 ounce (100 gram) serving of Vital Choice sockeye salmon, albacore tuna, or silver salmon averages more vitamin D than the US RDA of 400 IU. Interestingly, our lab's results differ from those shown in the official USDA tables, which rank the vitamin D content of sardines just above salmon's.
These discrepancies result from variations in the genetics and natural diets of regionally distinct sardines and salmon (See "Why Does Sockeye Offer a Surfeit of Vitamin D?”). Regardless of the reason, we're happy to report that our salmon and tuna test so very high in this vital bone-health, anti-cancer nutrient.
And, evidence from animal and human studies suggest that the marine omega-3 fatty acids found only in fish and aquatic organisms—especially omega-3 DHA—help the body preserve bone mass, while diets high in omega-6 fats and low in omega-3s weaken bones, giving us another good reason to enjoy salmon and other fish high in long-chain omega-3s.
Study’s flaws preclude firm conclusions
The new WHI study suffered from several design flaws:
- On average, both groups were functionally deficient in vitamin D, to an extent unlikely to be redressed by the amounts of vitamin D used in the study.
- Participants in both groups were allowed to continue to take other medications that could affect the findings.
- Magnesium intake was not considered, but this mineral is also vital for bone metabolism and calcium absorption.
- About half were on hormone replacement therapy, and some were also taking osteoporosis medications.
- Three out of four participants were overweight or obese, which is another factor thought to protect bones. (The body responds to weight-bearing stress by bulking up its bones.)
- Possibly as a result of these confounding factors, the hip fracture rate among the placebo-taking control group was about half of what was expected, making the difference in fracture rates between the two groups less distinct than it might otherwise have been.
Calcium and bone health: a red herring?
The combination of vitamin D and calcium has long been recommended to reduce the risk of bone fracture for older people, particularly those at risk of suffering osteoporosis.
As a consequence, calcium pills rack up the biggest sales numbers, with a U.S. 2004 sales total approaching one billion dollars.
But findings like those of the recently published WHI study suggest that high-dose supplemental calcium intake (i.e., 1,000 mg per day) is no magic bullet for bone health.
The failure of high-dose calcium to prevent fractures in the WHI study to the anticipated extent fits with the fact that Asian women—who consume considerably less calcium than their American peers—experience bone fractures at about the same or lower rates as American women, despite displaying an equivalent, genetics-related risk of dangerously low bone density.
These ethnic/geographic differences in fracture rates may relate more to variations in exercise than to nutritional distinctions.
For example, the Asian Osteoporosis Study (AOS), published in 1989 by researchers at The Chinese University of Hong Kong, found that bone fracture rates were highest in the three most urbanized and sedentary populations studied (US, Hong Kong, Singapore).
This finding suggests that lack of weight-bearing exercise is a more important risk factor than is low calcium intake, because Asians, especially those in less urbanized areas, consume far less calcium than Americans do.
In fact, high calcium intake may be less important than three other key factors affecting bone strength:
- Vitamin D: The body needs adequate amounts of this overlooked nutrient in order for bones to absorb calcium, but Americans consume and manufacture far too little, given the lack of dietary fish—the best source by far—and inadequate sunlight exposure resulting from today’s indoor lifestyles. (The body makes vitamin D when UV sunrays strike the skin.)
- Exercise: Bones only gain significantly greater strength in response to weight-bearing, bone-stressing exercise, which few Americans get enough of.
- Protein: A long-standing myth held that high protein intake could weaken bones by inducing an acidic status that could cause the body to take calcium from bones to balance its pH. In fact, higher protein intake correlates with lower risk of bone fractures, in part because dietary proteins raises body levels of IGF-1, a hormonal growth factor that promotes muscle and bone formation.
Letters to NY Times critique study conclusions and characterizations
On February 26, the New York Times published several letters from health care professionals who criticized the study’s design and assumptions, its authors’ conclusions, media mischaracterizations of its findings, or all three.
We thought we’d run excerpts from three letters the Times received from experts in the field (key points underlined for emphasis).
NYT Letter #1
Well, the Women's Health Initiative study did it again: it frightened and confused women. First it was hormones; now it's calcium supplements.
If calcium is to cause a significant reduction in fracture rate, the calcium must be directed by the body to go into the bone. Weight-bearing exercise is the primary way for bone to pull needed calcium out of the bloodstream.
So if a woman sits at a desk or in front of a TV all day (as many elderly women do), the bones cannot "tell" the body that they need calcium! The W.H.I. study seems to have left out this very important part of the equation.
We in the medical profession do all women a disservice when we don't stress that calcium supplements alone are not enough.
Teresa Schaer, M.D., Chief, Division of Geriatrics
St. Peter's University Hospital
New Brunswick, N.J., Feb. 20, 2006
NYT Letter #2
The editorial published with the calcium study notes that "several aspects of the study ... may have reduced the chances of detecting a benefit."
Many women in both treatment and control groups were already taking calcium and vitamin D supplements, and a hip-fracture benefit was found for those who had not been taking calcium and vitamin D.
Also, on average, both groups were clinically deficient in vitamin D at a level unlikely to be corrected by the amounts of vitamin D used in the study. Adequate magnesium, also vital for bone metabolism, was not addressed at all.
Dana Reed, MS, CNS, CDN
New York, Feb. 19, 2006
NYT Letter #3
Should it really come as a surprise that calcium and vitamin D supplements taken by postmenopausal women produced almost no reduction in the risk of fractures and little improvement in bone density?
The skeletal system grows rapidly during childhood and even adolescence. Bone mass developed during this period provides a reservoir from which we draw as we age and as our bone mass inevitably shrinks.
Does this study hold a lesson for us? Our children and teenagers are substituting soda for milk and sedentary TV for bone-building exercise. Don't be astonished if 40 years from now, The New York Times reports on an epidemic of osteoporosis similar to its recent series on diabetes.
Again, intervention will be too late.
Bernard Weiss, Ph.D., Professor of Environmental Medicine
and Pediatrics, University of Rochester
Feb. 19, 2006
Fractures follow falls: can vitamin D help keep you on your feet?
Lost in the headlines about the WIH trial were the intriguing results of two placebo-controlled clinical studies—one in Switzerland and one in Australia—that examined the fall-prevention benefits of supplemental calcium and vitamin D.
Before we describe their findings, it is critical to understand the obvious—but often overlooked—fact that that people don’t usually suffer bone fractures unless they fall. And risk of falling rises sharply if you are over 65 and sedentary.
Accordingly, anything that prevents falling can be as or more important than interventions that increase bone mineral density, such as calcium, vitamin, D, protein, and weight-bearing exercise.
Swiss anti-falling trial combines calcium and vitamin D
The results of this placebo-controlled trial were published last month by researchers from University Hospital Zurich (Bischoff-Ferrari HA. 2006) and Tufts University in Boston.
The participating 199 men and 246 women were put into subgroups according to levels of physical activity, and all took either supplements containing 700 IU of vitamin D plus 500 mg of calcium, or placebo pills.
After three years of taking a daily supplement of vitamin D and calcium, the rate of falling among active elderly women dropped by almost half, and was reduced by almost two-thirds in inactive elderly women (The pills had no effect on the rate of falling among elderly men).
These results suggest that inactive women benefit the most from calcium and vitamin D, in terms of reduced rates of falling.
These encouraging results support those of a previous study by the same research team, which showed a 60 per cent reduction of fractures in subjects taking the same dual-supplement regimen.
The Swiss-American research team surmised that the stark difference between the sexes could be due to the fact that women usually have lower muscle strength than men, and were therefore more likely to fall absent the as yet unexplained fall-preventive effect of the vitamin D-calcium regimen.
These results suggest that the difference between the number of falls of active and less-active women is due in part to the supplements, but also to the fact that the more active women put themselves at increased risk simply by being more active, so they stand to benefit more from any bone-strengthening nutritional intervention.
The researchers believe that the results have clinical significance. As lead author Heike Bischoff-Ferrari said, "We show a significant reduction in the odds of falling in ambulatory older women with a very inexpensive, well-tolerated, and simple supplementation with cholocalciferol [vitamin D]-calcium.”
The recent WHI study also supports these results, despite widespread misrepresentation in news reports. As we noted, women who actually adhered to the supplementation program enjoyed a 29 per cent reduction in fractures.
Aussie study isolates vitamin D’s fall-prevention power
The findings from a recent, placebo-controlled Australian trial (Flicker L, 2005) dovetail with the results of the Swiss-American study, and appear to award most of the anti-falling effect to vitamin D.
In the two-year trial, elderly nursing home residents took 1,000 IU of vitamin D (much more than the 400 IU used in the WHI study) or a placebo pill, plus 600 mg of calcium (much less than the 1,000 mg used in the WHI study), daily.
Since the calcium dose was relatively low, and the vitamin D dose was relatively high, it seems logical to attribute most of the benefit to the vitamin.
As the authors concluded, "Older people in residential care can reduce their incidence of falls if they take a vitamin D supplement for 2 years even if they are not initially classically vitamin D deficient.”
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