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High-protein diets and hypercalciuria, a negative calcium balance

Early studies that focused on the role of a high-protein diet in causing hypercalciuria, a negative calcium balance, increased bone resorption, and increased fracture risk are reviewed. Finally, evidence that a low-protein diet impairs calcium absorption and could negatively impact skeletal balance is summarized. Also see the news article about study of vegans and bone density: Vegans Have Lower Bone Density: Discovery News. The issue is that calcium is only one factor to consider when it comes to bone loss.

High-protein diets and hypercalciuria, a negative calcium balance.
Anne Hart, photography.

Researchers suspect that lower levels of calcium, needed for bone formation, in the diets of vegans results in lower bone density compared with non-vegans. The point to consider is that overall calcium is only a small contributor to bone density. What scientists need to do when reaching the public via news articles is to point out what other factors contribute to bone density, especially what factors contribute most to bone density in older adults, especially in women.

Vegans have lower bone densities than non-vegans, say Australian researchers

It's not clear why women have higher bone loss than men. Also see, Vitamin B12 Linked to Osteoporosis and Bone Loss in Vegetarians. Both vitamin B12 deficiency and weakening of bones are known to occur frequently in vegetarians. However, a direct association between the levels of vitamin B12 and bone weakening has not been reliably established.

In this study, weakening of bones was measured by assessing the blood levels of substances called bone turnover markers (BTMs). These levels are elevated in blood whenever there is increased bone destruction. In addition, levels of vitamin D were also assessed. The researchers found that, “low vitamin B12 status is related to increased bone turnover in vegetarians which is independent from vitamin D status.”

You may wish to see the article, Dietary protein, calcium metabolism, and skeletal homeostasis. Of concern are several recent epidemiologic studies that demonstrate reduced bone density and increased rates of bone loss in individuals habitually consuming low-protein diets. Studies are needed to determine whether low protein intakes directly affect rates of bone 'resorption,' bone formation, or both.

There's a great need to change the scoring system for heart disease

How calcified are you, and how dense is your calcification? Coronary artery calcium, known as CAC, is present in more than half of middle-aged U.S. residents; by age 70, its probability exceeds 90 percent. Now a new study demonstrates need to change scoring system for heart disease because the researchers found that dense heart plaques may have protective quality.

The study led by researchers at the University of California - San Diego School of Medicine shows that one of the most widely used systems for predicting risk of adverse heart events should be re-evaluated. A surprise finding was that coronary artery calcium (CAC) density may be protective against cardiovascular events. The study of CAC will be published in the January 15, 2014 issue of the Journal of the American Medical Association (JAMA).

What's protective?

Great CAC density of calcified plaque in the coronary arteries was inversely and significantly associated with risk of coronary heart disease and cardiovascular disease (CVD) events, said lead author Michael H. Criqui, MD, MPH, of the Department of Family and Preventive Medicine at UC San Diego, according to the January 13, 2014 news release, Study demonstrates need to change scoring system for heart disease.

"Current scoring systems assume that denser heart plaque (CAC) is more hazardous, but we found the opposite," explained Criqui, in the January 13, 2014 news release, Study demonstrates need to change scoring system for heart disease. "It's not good to have CAC but it is less hazardous if it's more dense."

The standard CAC score is called the Agatston

According to the National Heart, Blood and Lung Institute, the score is based on the amount of calcium found in a patient's coronary arteries. Traditionally, the test is negative if no calcium deposits, or calcifications, are found in the arteries, and interpreted to mean that the chance of the patient having a heart attack in the next 2 to 5 years is low.

The test is positive if calcifications are found in the arteries. Calcifications are a sign of atherosclerosis, a condition in which the arteries harden and narrow due to plaque buildup. The higher the Agatston scores are, the more severe the atherosclerosis.

"However, our study shows that in addition to CAC volume, the role of CAC density should also be considered when developing a risk score," Criqui said in the news release. "A greater volume of CAC does indicate a higher risk, but at any given volume of CAC, a higher density is associated with lower risk. This may be because densely calcified plaques are more stable."

Next step is diet evaluation

He added that since the dense plaques pose less risk, researchers need to look at what factors are related to denser plaques, adding that statin drugs appear to increase CAC density. The next phase of Criqui's research will include evaluation of the effect of diet, exercise and medical management of CVD on plaque density. Another focus will be developing an improved CAC score to incorporate density and other variables.

The study looked at 3,398 participants at six U.S. sites from four ethnic groups: non-Hispanic white, African American, Hispanic and Chinese, aged 45 to 84 years who were free of known CVD at baseline, and had CAC greater than zero on their baseline CT. The study participants were followed up through October 2010.

During a median of 7.6 years of follow up, there were 175 coronary heart disease (CHD) events, such as myocardial infarction, resuscitated cardiac arrest or death, and an additional 90 other CVD events, such as stroke.

Researchers study density

According to the researchers, measurement of CAC has consistently proven to be the best sub-clinical CVD measure in terms of improving CHD risk prediction. However, their study data suggest that the Agatston area or volume scores alone are not optimal measures to use in CVC risk prediction, since the demonstrated inverse association with density also needs consideration.

Criqui added that the data are consistent with numerous prior observations, including a modest correlation between CAC and coronary stenosis, or narrowing of the arteries due to fat or cholesterol. Previous studies have shown that patients with stable angina – chest pain caused by insufficient blood flow to the heart – were more likely to have calcified plaque than patients with unstable angina, which is more likely to lead to a heart attack.

Additional contributors to the study included Julie O. Denenberg, MA, Jochim H. Ix, MD, MAS, Dena E. Rifkin, MD, MS, and Matthew A. Allison, MD, MPH, of UC San Diego; Robyn L. McClelland, PhD, University of Washington, Seattle; Christina L. Wassel, PhD, University of Pittsburgh; Jeffrey J. Carr, MD, Vanderbilt University; and Matthew J. Budoff, MD, Harbor-UCLA Medical Center, Los Angeles.

The study was supported the National Heart, Lung, and Blood Institute, part of the National Institutes of Health (N01-HC-95159, N01-HC-95160, N01-HC-95161, N01-HC-95162, N01-HC-95163, N01-HC-95164, N01-HC-95165, and N01-HC-95169).

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