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Dem Bones

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Back in February, 2013 this blog looked at the positive association between calcium intake and the risk of all cause death rates and cardiovascular disease in women.  Older people have historically been encouraged to obtain their calcium from dietary sources instead of supplements.  A recent systematic review of randomized controlled trials as well as observational studies by Mark Bolland et al. concluded that there is no association with dietary intake of calcium and risk of fracture. Moreover, these authors found that the association between calcium supplements and fracture risk is similarly weak.

Interestingly, there are only two randomized controlled studies of dietary calcium intake and fractures. Contrary to RCT evidence, there are 50 reports from 44 cohort studies on the relationship.  In adults older than 50, for most studies (> 75%) , no relationship between dietary calcium intake, including milk or dairy sources, and fractures of the hip, spine or forearm could be confirmed.

In randomized studies, the degree of total fracture reduction associated with supplemental calcium was statistically significant with an 11% reduction (95% CI, 0.81, 0.96). However, the clinical importance of this reduction is uncertain.  When examining this relationship with specific fracture types (hip or forearm fractures), a statistically significant reduction could  not be demonstrated.  One trial1 in frail elderly women in residential care with low dietary calcium and low Vitamin D levels, did show decreased fracture risk (but 6 other similar trials that did not.)

So, most of the studies were observational and suffer from the inherent risk of bias.  It seems to me, the blogger, that there should be some level of calcium intake that is necessary.  Where too much is unhealthy, zero intake would seem to be unhealthy as well (reductio ad absurdum).  Nonetheless, we clinicians are caught calcium carbonate and a hard place again.

What’s a doctor to do?  Well, it starts with our pediatrician and family physician colleagues.  Put the calcium in during growth.  Even after they stop growing taller kids continue to make more bone than they lose.   Bone mass peaks somewhere between 18 and 25.  Seek to dispel parental concerns (and self-diagnoses)  of lactose intolerance in those less at risk (more common in the elderly, Blacks, Asians, Hispanic, and Native Americans but much less common in Northern Europeans).   Being products of the Kool-Aid generation, we missed out on this little piece of advice and are paying for it now.

 

  1. Chapuy MC, Pamphile R, Paris E, et.al Combined calcium and vitamin D3 supplementation in elderly women: Confirmation of reversal of secondary hyperparathyroidsism and hip fracture risk :  The Decalyos II study.  Osteroporosis Int 2002;13:257-64.

Radiation risk

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The Biologic Effects of Ionizing Radiation report was initially requested by the U.S. Environmental Protection Agency in 1996. Since then, there have been several revisions of the BEIR report, the last being the BEIR VII Report in 2005. BEIR VII was different in that it also looked at the effects of low dose (<100 MSv) radiation on humans.

BEIR VII estimated a 1:1000 risk for cancer from one 10 mSv exposure to radiation. This is the radiation exposure from one abdominal, pelvic, or chest CT. These are imaging studies we order very commonly in our practices. In fact, there were over 70 million CT scans ordered in the United States in 2007 with projections that this may cause 29,000 future cancers.

No one really knows whether there is significant risk from one CT scan. These estimates of risk are based on an analysis of large populations over time using a linear non-threshold extrapolation. However, even if the risk from one scan is small, it is not insignificant and people are exposed to so many studies over a lifetime.

Background exposure to natural radiation in the United States is about 3 mSv per year (mostly from radon). In 1980, the average radiation dose per person in the U.S. from all sources was 3.6 mSv per year. However, by 2007, the average dose in the U.S. had nearly doubled to 6.2 mSv per year. CT scans have become the biggest source of radiation exposure to humans after background radiation.

The risk of cancer varies by age and gender. The risk of cancer is much higher for those under 20 years of age and for females. We need to be especially careful in imaging children. There are over 7 million CT scans performed annually on children in the U.S. Pediatric radiologists practice ALARA (as low as reasonably achievable) in imaging children, but nothing is better than judicious ordering to protect our children.

Age 5 10 20 30 40 50 60
Male 1:557 1:692 1:1024 1:1458 1:1543 1:1692 1:2045
Female 1:296 1:383 1:608 1:939 1:1129 1:1351 1:1706

Estimated life-time risk of cancer, BEIR VII Phase 2, 2006

The radiation dose our patients receive varies by the type of study. Although plain films do not expose our patients to large doses of radiation, a CT of the abdomen or a barium enema is equivalent to about 750 chest x-rays, or more than 3 years of background radiation.

radiation risk

So yes, we need to be careful in ordering CT scans or other high-dose radiation imaging for our patients. This is our problem since the best predictor of radiation exposure in a population is the number of physicians in practice in that community.

Jim Cotter, MD MPH

Bye-bye bimanual

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When I was the medical director of the Sonoma County Public Health outpatient clinics, which included the Family Planning and STD clinics, I would commonly discuss the lack of need for a bimanual exam of the, typically, young women who used our services if they Continue reading →