I am not sedentary and have never smoked.   I started running in my 30s, and developed a joy in fitness that was expressed in both aerobic and weight-bearing ways. Exercise became a daily routine, almost a necessity, which contributed richly to my life without controlling it. Long ago I developed a taste for low-fat, nutritious food. Long ago I added calcium to my regimen of supplements. But I am slight of build, and favor my father’s mother. Recollection of her frail, bended frame has always haunted me. 

Most people fear some physical impediment above others. My terror has always been that my eventual fate is to shrink, to twist into painful immobility, trapped inside a bony, misshapen, easily-shattered shell. At the age of 47, still menstruating, still active, still purposefully directed toward health, I arranged a bone-mineral density (BMD) scan. It is a fairly fast, painless procedure. One lies supine as the x-ray device scans pelvis to ribs and a bony image emerges on a nearby computer screen.  I wanted to allay my fears.  

The report was cryptic but intelligible. T-scores compare bone density of the patient with that of a normal 30-year-old. The World Health Organization defines osteopenia as bone-density T-scores of more than one, and less than 2.5, standard deviations below the mean; osteoporosis proper exceeds 2.5. With each standard deviation below normal, risk of fracture approximately doubles.   Evaluation of my lumbar spine yielded  a T-score of two and one-third standard deviations below that of normal bone density.   The diagnosis was osteopenia, the preface to  osteoporosis.  The presence of estrogen failed to prevent a premenopausal bone fragility,  and the fate I feared was waiting in the wings.   But why?  

Partial reasons present themselves.   I was a thin child and, with anything but spaghetti, an indifferent eater.   As a teenager, I fell headlong into all the fast-food traps, and all through my 20s my eating habits were erratic; thus, at the most important times of bone development, long before cultivating my taste for nutritious food, my dietary habits failed me.   Family history is always important, and my grandmother provided genetic reason.   There may be other hidden genetic reasons as well, such as possible problems in utilizing vitamin D or calcium.   Topical corticosteroids I have used for years on eczema might have contributed a small part.   The average onset of menses in girls is at the age of 12; mine occurred not until the age of 16, and such pubertal delay might have its own detrimental effect on bone mass.  For reasons still being explored, even a history of depression, for which I qualify, has recently been connected with osteoporosis.  If my search for answers has not brought one immutable reason, at least any unbounded faith in my current and longstanding (but not longstanding enough), exertion-filled, vitamin-popping lifestyle is restrained.  

Remodeling is constant in adult bone:  At the cellular level, osteoclasts destroy and osteoblasts rebuild it.   The process renews and repairs.   But as we age, rebuilding slows. Knowing that, we seek calcium and consider ourselves safe.   Many drink milk.   Although milk contains plenty of calcium, by deactivating critical enzymes pasteurization prevents our bodies from  incorporating that source of calcium.   Actually, the belief that calcium protects against bone loss is flawed.   Even with vitamin D, even with magnesium, calcium is not easily absorbed, and even if it makes its way to the bloodstream its integration can be complicated by genetic traits, including variations in vitamin D receptors, that are just beginning to be understood.   Studies have plotted the decline of bone mass in women who religiously swallow their calcium supplements.

Today, however, we are fortunate.   We have remedies.