Wednesday, August 28, 2013
Should I take calcium? Part I
I have been reading up on that which is good for blood vessels versus that which hastens their demise. In particular, owning a set of bones increasingly fragile with age, I was curious about the effects of calcium supplementation on vascular health. Recent headline news from the latest medical research suggests that excess intake of calcium tablets results in deposition of calcium in the walls of arteries--not something you'd wish on your hardworking vessels. I used to recommend adequate calcium intake as an integral part of the prevention and treatment of age-related bone loss-- 1,000 mg/day total (diet plus supplements) if on hormone replacement and 1,500 mg/day if not. Now the US Preventive Services Task Force says no. In fact they give a calcium plus D supplementation strategy a "D" grade (which is very strong language for the USPSTF) based on the increased risk of kidney stones but mentioning not at all this vascular business. Uptodate.com--a widely used on-line resource for physicians says yes.
What's an old lady to decide? Do I recommend extra calcium for myself and for others?
After two hours of reading, I realized this was a decision so complex that it could not be answered in a single day nor a single post. I decided to approach the problem according to the 8 components that I believe are the basis for making medical decisions. In brief, I think physicians bring three areas of expertise to the process--the science, the evidence from a constantly changing body of medical literature, and their personal practice experience. Patients (and in this case I'm filling both roles) bring their current situation, their personal medical history, their family history, and their beliefs to the table. Finally, and unfortunately, the insurance company brings its willingness to pay into the picture. This is not important here as calcium and D supplements are not an insurance-covered benefit.
A steady level of circulating calcium in the fluids and blood surrounding our cells is essential to the proper function of multiple organ systems, especially normal nerve conduction. Too little can cause spasms, seizures, and abnormal heart rhythm; too much leads to confusion, coma, and abnormal heart rhythm. As a result, a wonderfully orchestrated system controls serum calcium by balancing incoming sources from both intestinal absorption and internal release from bones with outgoing losses through the colon and the kidneys. If your serum calcium level is normal on your lab panel, you can thank your intestines, kidneys, bones, and parathyroid glands, but you cannot assume that your calcium intake is adequate nor that your bones are holding up okay.
In order to maintain that crucial balance, calcium in to the extracellular fluid (ECF) must equal calcium out. Your parathyroid hormone levels rise in response to decreased ECF calcium which quickly leads to release of bone calcium. In the short term, only superficial bone layers are involved in the release of mineralized calcium from the bone structure, and this loss is easily replenished. On the other hand, a negative calcium balance over time, amplified perhaps by vitamin D deficiency or an age-related drop in estrogen and testosterone, can lead to a loss of bone density progressing to osteopenia and osteoporosis.So calcium balance is critical to bone density along with many other functions. There are many conditions which can cause abnormal calcium levels, but what we are considering here is the situation of an otherwise healthy aging person trying to maintain bone health through calcium intake without increased risk to the cardiovascular system. The next post will cover the evidence with regards to calcium intake and bone health.