BONE PAIN IN CHRONIC KIDNEY DISEASE


Bone Pain in Chronic Kidney Disease

Most members of Club CKD are well-acquainted with that debilitating knee or lower back pain which intensifies as kidney failure approaches.

Your medical team gets your bloodwork done & may be able to relate this pain to desperately low levels of Vitamin D!
(provided you don’t already have a separate bone or nerve condition)

But we’re talking about Chronic Kidney Disease, right? What does Vitamin D have anything to do with it? And how does that cause you bone pain? Let us try & dissect this topic, shall we?

VITAMIN D & KIDNEYS

Although highly, under-appreciated, perhaps because they are relatively “quiet”, our kidneys are supreme powerhouses! Among the many functions that it performs, turning “Vitamin-D into its Active, Usable form” is a crucial one.

PRODUCTION OF ACTIVE FORM OF VITAMIN D

When we talk of obtaining Vitamins for our body functions, we mostly point to their respective food sources. But Vitamin D is special. That’s because the bulk of it is literally produced in our body! Because of this fact, nowadays, the medical research community also recognizes Vitamin D as a Hormone. That is not to say there aren’t any food sources for Vitamin D, but the majority of what we need daily is usually created in our bodies itself.

Let’s call this process, “The Vitamin D Synthesis Movie”. The lead actors here are Sunlight, Our Skin, Liver and Kidneys!

Bone Pain in CKD
Production of Active Vitamin D by the Kidneys

Our skin layers normally contain a chemical called 7-Dehydrocholesterol in them. The common name for this is “Pro-Vitamin D3”. When we go out & about on sunny days, the less harmful part of the ultraviolet rays in sunlight finds its way to Pro-Vitamin D3 in our skin and “coaxes it” to transform to Vitamin D3.

This is not usable by the body as such. So, our blood diligently carries Vitamin D3 from Skin to the Kidney via the Liver in between. Both at the Liver & the Kidneys, specific Enzymes sequentially act on Vitamin D3 to finally turn it into an Active, Usable form of Vitamin D that can be safely diverted for its many useful roles in the body.

WHAT MAKES ACTIVE VITAMIN D IMPORTANT?

In good health, this Active Vitamin D helps retain optimum Calcium levels in our blood. It does so, by absorbing it from digested food passing through our intestines and from our urine as per need.

Bone Pain in CKD
Active Vitamin D “hand-holds” Calcium from digested food in the Duodenum (intestine) and takes it to the blood

To put things in perspective, imagine Vitamin D floating in the bloodstream, “waiting” outside our intestine (small bowel) for a food ball to pass through. The desire to meet & greet Calcium is such in Vitamin D, that it is capable of effectively “sensing Calcium across intestine walls” as soon as it is about to pass by.  Once this happens, Vitamin D literally “makes way” through the intestine wall & “hand-holds” the Calcium in digested food within the intestine to carry it out and deliver it to the bloodstream. That is precisely how Active Vitamin D helps pump-up and maintain normal blood Calcium levels.

A normal blood calcium level means healthy heart, muscles, nerves, bones & teeth. And all these organs can safely thank their kidneys (where Vitamin D is activated), for their happy times!

WHAT HAPPENS IN CHRONIC KIDNEY DISEASE?

When chronic kidney disease damages the specific kidney cell types that produce Alpha-1-Hydroxylase – the enzyme that turns Pro-Vitamin D from Liver into an Active, Usable form of Vitamin D. As a result, the necessary enzyme levels drop. And this jeopardizes kidney’s “ability to activate Vitamin D”. In a nutshell, our in-house machinery that retains blood Calcium levels is severely impacted.

Now, we all have heard of the butterfly-shaped Thyroid gland in our neck, haven’t we? Within the thyroid, there are four other button-like glands found embedded, one on each corner. These are the Parathyroid glands.

Bone Pain in CKD
Image Source: http://www.yourhormones.info/endocrine-conditions/secondary-hyperparathyroidism/

These glands produce a hormone called “Parathormone” or PTH which normally assists Active Vitamin-D to pump-up blood Calcium levels. So, when Parathyroid glands sense the Vitamin D crisis brewing in advanced stages of CKD, they “offer to help”. However, they do so chiefly by “borrowing” Calcium from bones!

Now with normal Vitamin-D levels in good health, Parathyroid glands simply need to maintain somewhere between 10-65 ng/L of PTH hormone in blood. These normal levels deter PTH hormone from bothering bones without good reason. However, with an almost alarming deficiency of Active Vitamin D in Kidney Failure, the Parathyroid Glands get over-enthusiastic about helping blood & end up unleashing abnormally high levels of PTH hormone. This level can vary between 300-700 ng/L unless suitably treated.

The fancy medical term for such a situation is Secondary Hyper-Parathyroidism.

[Secondary, because PTH levels rise due to indirect causes such as low Vitamin D levels and NOT directly due to a condition in parathyroid glands; Hyper meaning “high”; Parathyroidism referring to “of parathyroid gland”.]

Although the intention of Parathyroid Glands is clean (?), high levels of PTH hormone literally chew-off excessive amounts of Calcium from bones! As a result, bones begin to turn fragile & prone to fractures. The weakened bones are unable to bear our body weight effectively, and they complain about their plight with “Bone Pain”.

NOTE:

The joints that bear the most of our body weight such as lower back, hip & knee joints are the worst sufferers of this “unwanted charity” by PTH! So, these are the bone joints where CKD patients report most cases of bone pain.

Here is a Graphic elucidating the whole Bone Pain Fiasco arising out of Vitamin D deficiency in advanced CKD for you to refer to.

Bone Pain in CKD
Bones bear the brunt of low Vitamin D levels in Kidney Failure

Now that you understand, the why & how of Bone Pain in CKD, you are fully prepared to grasp how the treatments for this condition work. Team ATK will come up with a comprehensive explanation on this topic for you in the next article. Till then, don’t stop asking questions about your health. The more clarity you gain about it, greater will be the relative peace of mind during your CKD journey.


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