Circadian (13): Tests

If you are still floating around in the vast ether after my last article, today I would like to bring you back onto planet Earth and deal with some hard physical realities. You might feel tired, sluggish, emotional, or drained. Or perhaps you have some physical symptoms no one has been able to help you with. You are not sure if you have a good sleep-wake pattern. You might be asking: how do I know if my body’s circadian rhythm is in sync with everything it needs to be in sync with? Is there a simple and reliable test my doctor can do?

The short answer is yes; there are simple tests for circadian rhythm assessment. The keyword ‘simple’ rules out polysomnography (i.e., a sleep study), let alone the challenge of how to interpret it. Salivary and 24-hour urine tests are in this excluded group too, disqualifying meaningful melatonin and cortisol quantification. You would think that Vitamin D is in the ‘simple’ group, except that it has too many variables affecting the test, such as time before last UVB exposure, dietary and supplement intake, heterophile antibodies, alcohol and smoking habits, body habitus, expression of VDR, liver and kidney health, availability of retinol, and use of prescription medications. And that is, of course, if the right metabolite is tested (cholecalciferol, ergocalciferol, calcifediol, calcitriol, or their sulfated forms). Let’s agree that it is not that simple.

When it comes to body clock assessment, after a rigorous history taking, I normally use the following to prove or disprove my suspicion of a disrupted circadian rhythm: PTH, ASCA, rT3, and Leptin. The tests are only as perfect as your practitioner’s interpretation of them. Forgive me for the digression, but this reminds me of a colleague online who publicly stated that an alternative test is not "evidence-based." That is an oxymoron, as tests are never the evidence. Our interpretation of them makes the evidence. If you are a professional and you come across a test that you have no clue how to interpret, it might be wiser to stay away from making comments beyond: "I’d better skill up."

Fortunately for everyone, the four tests I named above are all part of conventional science (which is really all I do) and can be tested at your standard local pathology provider. It doesn’t mean, however, that your conventional doctor will understand them—how they came about, what they mean, and what can affect their levels. I totally doubt that your non-conventional practitioners will know them inside out either; but really, unlike conventional doctors, those with non-conventional qualifications don’t often claim or project that they do. These tests essentially reflect the clock of your bones (PTH), gut (ASCA), thyroid (rT3), and adipose tissues (Leptin). Essentially, you test them against a master clock or an anchor—sunrise is a good one—and decide if they are in sync with it or are running adrift.

PTH, short for parathyroid hormone, is my favorite by far. I like it because bone activity and metabolism are predictable. Don’t confuse it with thyroid hormone, as the two couldn’t be further apart. This bone metabolism hormone is only called "parathyroid" because the glands it originates from are very close in proximity to the thyroid organ. If you are where I am, in Bundaberg, or any latitude closer to the equator than Bundaberg, then your fasting morning PTH should remain below 3.0 pmol/L all year round. Anything higher than this necessarily means that your bones are running on a different clock to your brain.

I appreciate that, if you are a doctor reading this, your reaction might be that I have made all of that up. But have you ever wondered who decided what level was a "normal" level for PTH? Just because a lab report inked 1.6–6.9 pmol/L as a ‘normal range’, does it mean the scientific publications will race to support this idea? Or should it be the other way round—that the ‘normal range’ changes with our improvement in understanding the body? Better still, isn’t "normal" dependent on context and the unique patient in front of us? You see, when dealing with parathyroid cancer, any PTH below 30 pmol/L is reassuring. But if you are querying parathyroid adenoma, you want to see the level sitting well below 9 pmol/L. However, for bone turnover, it had better be below 5 pmol/L. When it comes to the body clock, depending on season and latitude, you want PTH to be between 1.2 and 5 pmol/L. After thyroid surgery, it may be normal for PTH to hover between 0.5 and 1.5 pmol/L. My point is, we have to understand science. And that does not include putting blind faith in a laboratory’s reference range.

Essentially, PTH works in a see-saw relationship with bioavailable vitamin D (high PTH = low D, and vice versa). I say ‘bioavailable’ to exclude supplemented vitamin D, as various human studies have failed to show a linear PTH response to this form of vitamin D. How it works is that when the vitamin D made in our skin reaches the gut, it opens the doors that can accept calcium for absorption. Without vitamin D, the doors are shut and there is very little chance for any calcium absorption from the gut. This is when PTH takes matters into its own hands.

Our bloodstream needs to maintain a tight level of calcium at all times to ensure proper cellular functioning. If there is no calcium coming in from the gut due to sunlight deficiency, there has to be a back-up method, albeit imperfect, to keep the supply going—or we risk imminent death from low blood calcium within hours. The parathyroid glands secrete PTH, which goes to the body’s massive reservoir of calcium: our bones. PTH borrows calcium from the bones to keep us going until the next time we see the midday sun. Naturally, as there is often sunlight and darkness in succession, our PTH goes down in the day and up at night. This entrainment has happened over hundreds of thousands of years and is seen across all animal species which interact with the sun. But, again, we conveniently came along, and within a few decades, we managed to break this very fundamental ‘habit’ that our biology has preserved for so long for our own good.

So when I see a morning PTH result of more than 3.0 pmol/L, it either means that the person’s bones are still at "night" when it is morning, or that the bones are convinced they live in a Sydney winter despite the mind’s belief in its Bundaberg subtropic existence. Neither is ideal; both are harmful to our health downstream.