How Does Secondary Hyperparathyroidism (SHPT) Affect My Kidney Disease Diet?
First, let me explain what SHPT is. Your parathyroid glands are responsible for keeping your bones and calcium levels in your blood at a healthy range. They are located in your neck on the back of your thyroid gland. Most of the time, you don't even know they are there. They are near your thyroid gland, but work separately and produce PTH (Parathyroid hormone). PTH is responsible for maintaining the correct amount of calcium in the blood and bones, as well as ensuring calcium is absorbed from the digestive system, and finally controlling how much is excreted in the urine. (That is the connection to kidney disease). The amounts of other minerals that are part of bone growth – phosphorus and Vitamin D – are also critically important to the parathyroid. Doctors measure the amount of PTH as an indicator of bone disease.
Secondary Hyperparathyroidism (SHPT) as related to kidney disease is an overproduction of PTH. This is caused by the changes in the kidneys affecting other mineral levels in the blood and causing the body to overproduce PTH. In persons with CKD starting in stage 3, damage to the kidney affects the functioning amount of kidney and cause these changes to possibly occur.
What Causes The Body To Produce More PTH?
While that is a complicated question, I would like to answer it in a way that is easier to understand. Please remember – I am not your doctor!
Initially, your functioning kidney mass is decreased. This happens because of the damage over time to the nephrons in your kidneys. Your doctor may have told you a percentage of your kidneys that are still functioning. Once the amount of your kidneys that are working is decreased beyond a certain level (not exactly clear how much and it varies by individual), 2 things happen.
1. Kidneys are responsible to activate the Vitamin D in our body so it works. With less functional kidney, lower amounts of vitamin D3 are available in the blood stream.
2. Kidneys also excrete the phosphorus in our bodies, and with a lower capacity to produce urine, phosphorus builds up in the blood stream.
Those two events that happen together bring about a decrease in serum (blood level) calcium. A decrease in the amount of calcium, plus a decrease in the amount of Vitamin D3 and an increase in the amount of phosphorus in the blood cause your body to think you need more PTH (because it needs to increase the amount of calcium in your blood stream to a normal level).
What Does Vitamin D Do In Our Body?
PTH works to “normalize” the amount of calcium available in your bloodstream. Calcium is used for many things in your body, and it needs to be available to your cells. So, an increased amount of PTH will cause your bones to be broken down more quickly so that the calcium is available in your bloodstream.
Vitamin D3 happens to be very important in the actions and levels of PTH in our body. You may be aware that our bodies can “make” vitamin D by exposing our skin to sunlight for 10-20 minutes every day. That vitamin D our skin makes has to be transported to the kidney to be changed into the “active” form our body uses. It keeps us from overdosing on Vitamin D with too much sunlight.
Once vitamin D becomes activated, it can work in our bodies. It stimulates some other hormones that tell the parathyroid we have enough PTH. It also decreases PTH indirectly by increasing the amount of calcium we absorb in our “gut” through our intestines. This increases the amount of calcium in our blood stream, and keeps the amount of PTH at a normal level. But once you have a decreased level of vitamin D in your body, it does not work to increase the level of calcium in your blood stream as efficiently (you don't absorb as much) so your body starts increasing the amount of PTH to accommodate your calcium needs.
How Do Our Bodies Handle Phosphorus?
When the eGFR decreases to less than 60 ml/min, your ability to remove phosphorus from your blood via your kidneys becomes altered. The part of your nephrons that are still working compensate by increasing the removal of phosphorus because your blood levels are increased. This helps to maintain normal phosphorus levels in your blood stream.
Once you progress further in kidney disease, your nephrons eventually become unable to excrete enough phosphorus to compensate, and that is when you start to notice hyperphosphatemia. (elevated blood phosphorus). So, as the amount of phosphorus increases in your blood, PTH is secreted to compensate. Calcium can bind with phosphorus (if they are out of balance) in the blood stream and form particles that then are deposited in organs and blood vessels. As phosphorus levels increase, this risk is higher, so your body reacts by breaking down bones and increasing the calcium levels in the blood stream to even out the levels. This causes the bones to be weakened over time, and calcium particles (those bound with phosphorus) to deposit in areas of the body such as the heart.
What Are The Goals Of Treating A Patient With SHPT?
Overall, the goal is to normalize the levels of the hormones and vitamin D so that the body is not breaking down bone to compensate for increased phosphorus levels. Preventing bone disease, called renal osteodystrophy, is key to the management of the disease. Patients with kidney disease are at a higher risk of cardiovascular disease, and calcium deposited in the heart can cause further problems.
In stage 3, it is very possible that the levels will be normal, but your body is working overtime to compensate and ensure that you are kept in that normal range. National KDOQI guidelines recommend that all patients with a eGFR < 60 ml/min/1.73m2 undergo an evaluation of serum calcium, phosphorus and PTH levels. KDOQI guidelines recommend testing once per year starting with the onset of Stage 3 CKD. PTH should be the key test for patients because of the way the body adjusts to keep calcium, Vitamin D, and phosphorus levels in the normal range by increasing the levels of PTH.
Management And Treatment of PTH and SHPT
KDOQI guidelines have recommended target ranges for PTH and calcium levels in patients with Stage 3 – 5 kidney disease. Based on those target ranges, the first course of action to improve the health of a patient with SHPT and suppress the levels of PTH is thought to be Vitamin D therapy. As vitamin D plays such a role in our absorption of calcium, if a person can take in and absorb appropriate amounts of “active” vitamin D (doesn't have to be processed by the kidneys), their calcium absorption rate should also improve.
In addition to Vitamin D, dietary therapy includes reduction of high phosphate foods. Foods that are high in phosphate content include dairy products, meats, beans, dark sodas, beer and nuts. Many of these foods are great sources of protein, so it is important to be cautious when eliminating foods. You should focus on removing foods that are high in phosphate yet lower in protein, such as dark colas, cheese, milk, ice cream and beer.
You have to be careful about sources of protein because that can lead to malnutrition which affects outcomes once people start on dialysis. Also, dietary phosphate restriction may not be adequate since most of our food contains phosphates. Many doctors also recommend the use of phosphate binders as well.
Phosphate binding agents are taken with foods, up to 3-4 times per day, and attach to phosphate in the foods we eat causing it to remain in the digestive system and be excreted through stool. They have to be taken with food or they don't work effectively, yet it is difficult for people to be consistent and remember to take the medications. Sometimes doctors use several different types of binders to achieve success. Some phosphate binders can be found over the counter such as calcium carbonate and aluminum hydroxide. But, you should talk to your doctor about it prior to initiating any additional intake.
What Should I Do About My SHPT?
First of all, discuss what it means with your doctor. Develop that relationship so you can ask. If you cannot, consider finding another doctor who will work with you. If you need to make a longer appointment, you should tell the person booking the appointment that you have a lot of questions and request a longer appointment time. That will keep your physician from feeling rushed.
At this point – if you have CKD Stage 3, it is recommended that you work with a nephrologist. They are experts and will manage your kidney disease very well. You may also want to find a local dietitian or check into a meal plan that meets your nutritional needs. Decreasing the amount of phosphate in your diet, in addition to treatment with an active vitamin D medication can provide a great deal of improvement and reduce your risk of bone and cardiac complications.
Thanks for sticking with me through this entire article. I enjoyed finding out what would help you and steering you in the right direction. If you enjoyed this article, you might enjoy one of my meal plans – Click here now to read more about Stage 3 or Stage 4 kidney meal plans.