Osteoporosis 5- Chronic Stress

There are 2 types of stress responses in our lives; a short term response and a long term response.  The short term response is considered to be governed by the sympathetic nervous system.  The long term response characteristically involves the release of glucocorticoids, namely cortisol. 

We've already discussed the fact that many people have overactive sympathetic nervous systems.  This has an immediate impact on bone.  We saw in a previous post that sympathetic dominance will inhibit osteoblast activity and increase bone resorption (breakdown).   In fact, much has been written about the more typical stress response seen in America; a prolonged short term response layered over an ongoing long term response.  It's worth noting here the influence of the long term response on bone health.

A 2008 paper does a good job describing the role of stress.
"Cortisol excess inhibits bone formation, increases bone resorption, impairs calcium absorption from the gut, and affects the secretion of several hormones (in particular gonadotropins and GH), cytokines, and growth factors, influencing bone metabolism." 

Remember that cortisol is considered a "stress hormone" and is released in times of physical, emotional or psychological stress.  It is a normal response but in a stressed out world, tends to get hyperactive.  The authors continue,

"Subclinical hypercortisolism, a condition of impaired hypothalamic-adrenal axis homeostasis without the classical signs and symptoms of glucocorticoid excess, is a recently defined entity, which has been shown to be associated to increased bone resorption, bone loss, and high prevalence of vertebral fractures regardless of gonadal status."

You could still ask, "is this common or a rare event?"  The authors conclude,

"recent data suggest that subclinical hypercortisolism is a common and underrated finding in patients with established osteoporosis."   J Endocrinol Invest 2008 Mar;31(3):267-76

There are scores of papers the describe the role of stress in degrading bone health.  Attempts to manage osteoporosis without considering the stress response will likely fall short.

Osteoporosis 3- Fight or Flight

The so called "fight or flight" response is mediated by something called your sympathetic nervous system.  It is considered your short-term stress response (your long-term stress responses is mediated by a different but very closely related system).  Many individuals experience chronic activation of this "fight or flight" system.  In reality, this physiological response is supposed to engage when needed and then turn off when there is no immediate need for it.  Unfortunately, our crazy world and busy lives often induce chronic activation of your sympathetic system.

For example, it is well known that obesity promotes excessive sympathetic activation.  We are still learning why this happens, but several ideas have been proposed.

"Several mechanisms have been proposed to explain the SNS activation in obese subjects; increased leptin concentration, hyperinsulinemia, obstructive sleep apnea, decreased arterial baroreflex sensitivity, elevated plasma angiotensin, obesity-related kidney disease and lack of exercise." Int J Hypertens 2011; Jan 20:642416.

Even in non-obese individuals, it is not uncommon to have excess sympathetic activation.  This is consistent with the dramatic rates of hypertension, fast resting heart rates, poor digestion, erectile dysfunction etc.  All these problems, while multi-faceted, have a layer of excess sympathetics.  Now let's consider bone health.

Does the sympathetic dominance commonly seen influence bone metabolism?  The answer is, yes.

"...increasing clinical and experimental evidence has driven attention towards the pivotal role of the sympathetic nervous system (SNS) in bone remodeling" Ageing Res Rev 2011 Jan 22.

"...sympathetic nervous system inhibits bone formation and increases resorption due to the binding of catecholamines to receptors located in osteoblasts."  Eur Rev Med Pharmcol Sci 2009 May-Jun;13(3):157-62

What does this mean for the average person concerned with their bone health?  It means calm down your sympathetic nervous system.  I realize this presents a big bag of worms that poses the question, "how do you calm down sympathetics?"  We'll address some of the science at a later point, but for now...a healthy lifestyle; eating lots of plants, regular exercise, stress management, lots of water and general avoidance of the "bad stuff."  I realize this isn't exactly a thrilling game plan.  But when you understand that a poor lifestyle influences bone health in a myriad of ways, it is my hope that that will be greater motivation for you to stick to it.  

If we were to stop this series right now, a healthy diet would help bones because:

1.  Decreasing sodium would decrease calcium excretion.

2.  You would calm down sympathetic dominance which would in turn, stop irritating the bones.

We'll continue on and expand our understanding of the many variables that influence bones.

Stress and epigenetics

I've written previously on the concept of epigenetics, the study of gene expression.  We know that for all intents and purposes, your genes do not change.  However, the little signals that tell your body when to express those genes (epigenetic signals) can be altered.  Food certainly has a powerful role in this although we do not understand all the details.  A recent paper also demonstrates that chronic stress will alter epigenetic markers.

Researchers at the Johns Hopkins School of Medicine found that the markers on genes were different after mice were exposed to stress hormones.  They believe that this may have a significant role in the development of  mood disorders.  Notably, the changes were found to be long lasting.  The epigenetic changes were presents for weeks even after the hormones had been removed from their environment.  In other words, these are potentially long lasting epigenetic changes.

 

"These behaviors, which were probably advantageous earlier in evolution, aren't as useful today with modern stressors that we can't fight or flee, such as work deadlines, Potash adds. Consequently, chronic stress might instead lead to depression or other mood disorders triggered by epigenetic changes."

I spend a lot of time talking about the benefits of eating good food.  But total health requires a life style adaptation as well.  Some people believe they thrive when under pressure; we even take pride in it.  Nobody can argue that some individuals genuinely do well under chronic stress. However, we must understand that your performance (at your job, school etc.) does not necessarily correlate with your well-being.  Chronic stress comes with a price.  Much of it has been well described (HPA dysfunction, hypercortisolemia etc.) We now have evidence that even your DNA expression may be altered by stress.