What might be Too Thin? and Why?

March 4, 2011 Leave your thoughts

Speaking to groups about Osteoporosis is always interesting.  Different persons have different questions.   This week I spoke to a PEO chapter (a women-only “sorority”).  One of the members was very fit and rather thin.  She wanted to know why she was at increased risk for Osteoporosis due to being thin.  Good Question!

Many studies have shown that a BMI of less than 20 is an independent risk factor for Osteoporosis, low BMD, and Fracture.  A BMI of 20 is 110# at 5’2″, or 120# at 5’5″, or 135# at 5’9″, or 160# at 6’3″. 

Medical doctors consider a BMI of 18.5 to 24.9 to be the ideal weight for heart health and diabetes health.  However, a study published 2 months ago confirmed what we have known since the 1950’s.  People with a BMI of 25 to 30 live the longest.   Why?

We do not know all the answers, but some suggestions are obvious. 

First, dealing with bone health.  Low Vitamin D, especially during the winter, is is a common finding in North America.  Since Vitamin D is stored in fat cells, thin individuals are likely to run low sooner than heavier persons.  The main source of Calcium in diet is dairy products, which are avoided because of fat content by many persons trying to stay thin.

These effects can probably be offset by taking enough Calcium and Vitamin D suppliments all year round.   Compensate for all the risk factors that you can. 

Weight, regardless of BMI, encourages stronger bones and muscles, which protect from fracture, up to a point.  Over a BMI of 35, weight overpowers muscle and bone to predispose to more fractures.

Away from bone health, most people lose weight while going through a major illness or serious injury.  Their bodies just cannot keep up with the additional metabolic needs.   Without sufficient additional fat and muscle to burn, you may not have enough reserves to survive a catastrophic injury or disease.  Fortunately these are rare.

Jay Ginther, MD

March 2011

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