Chapter 15: Vitamins, Trace Elements and Metals

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Welcome to the Deep Dive.

We're really glad you're here with us today.

For this session, we have a very specific mission.

You really do?

Yeah.

We are opening up chapter 15 of clinical biochemistry and metabolic medicine, the eighth edition.

So think of today as basically your own one -on -one tutoring session.

We're going to walk through vitamins, trace elements, and metals in the exact order they appear in the text.

Right.

So you can absolutely ace your clinical biochemistry exams.

Exactly.

We really want to bridge that gap between the textbook and the patient.

We'll look at the normal biochemical principles, how they support your understanding of pathophysiology,

and crucially, how those abnormal processes translate into the laboratory findings you'll actually have to interpret on the wards.

Okay.

Let's unpack this, starting right at the top.

What exactly are we talking about when we say vitamins and trace elements?

I mean, people throw these terms around constantly in the wellness space, but in a clinical context, they have very rigid definitions.

They do, yeah.

And precision really matters here.

Historically, vitamins were thought to be amines, which is actually where the term came from, vital amines.

But today, the strict definition of a vitamin is an organic compound essential for normal growth and development.

The defining characteristic is that the body either cannot synthesize it at all, or it just can't synthesize enough of it to meet physiological needs.

And trace elements.

Trace elements are similar in function, but they are inorganic compounds.

You only need them in minute amounts, specifically less than 0 .01 % of your body weight.

For the vast majority of people, a normal mixed diet provides entirely adequate amounts of both.

Wait, if a normal diet is entirely adequate, how often are we actually seeing true deficiencies?

And if hospital food corrects a deficiency that quickly, how narrow is our window to actually draw these diagnostic labs?

That seems like a massive trap for a busy clinician.

It is a huge trap.

What's fascinating here is the clinical protocol you have to follow.

You must draw the labs for a suspected micronutrient deficiency immediately.

Like before they even eat?

Exactly.

Before the patient resumes a normal diet in the hospital.

If you wait even a day or two, the lab results will often rapidly revert to a normal baseline just because of the hospital food.

Wow.

Yeah, and that completely masks the diagnosis.

If you miss that window or if the diagnosis is still ambiguous, sometimes the most reliable assessment is just an empirical trial of the micronutrient to see if the patient's symptoms actually improve.

So timing is literally everything.

Looking at the big picture, the text outlines four main pathways that lead to a vitamin deficiency.

First is inadequate intake.

In affluent populations, you usually only see this with unusual restricted diets, chronic alcoholism, anorexia nervosa,

or in patients who are strictly on artificial parenteral or enteral nutrition.

Right.

Second is inadequate absorption, which points you toward malabsorption states.

Third is excess loss, usually via the gastrointestinal or renal tracts.

And finally, enhanced utilization, where the body's demands suddenly skyrockets, like during sepsis or after severe trauma.

But we have to look at the other end of the spectrum too, vitamin excess.

Certain vitamins are highly toxic if they accumulate.

And unfortunately, clinical overdoses has become much more common recently.

Because of supplements, right?

Primarily because of the massive availability of over -the -counter supplements, yes.

We see this toxicity most frequently with vitamins A and D.

To understand why A and D can build up to toxic levels while others don't, we have to talk about solubility.

Vitamins are divided into two camps.

You have your fat -soluble vitamins, which are A, D, E, and K, and then your water -soluble vitamins, the B complex and vitamin C.

And the clinical relevance of this distinction is profound.

Picture a patient presenting with statorrhea.

That's the excessive foul -smelling fat in the stool.

Right.

Because they are malabsorbing fat, their body will selectively fail to absorb those fat -soluble vitamins, A, D, E, and K.

However, they will largely retain their water -soluble vitamins, with the notable exceptions of B12 and folate, which have their own complex absorption mechanisms we'll get into later.

That distinction sets up our journey through the fat -soluble group perfectly, starting with vitamin A or retinol.

Normally, you ingest precursors called carotenes.

Think of the beta -carotene in yellow and green plants like carrots.

Your intestinal mucosa hydrolyzes that beta -carotene into two active molecules of vitamin A.

It's stored in the liver and travels through the plasma bound to a specific carrier protein called retinol binding protein, or RBP.

Which is key for the labs later.

Right.

At a cellular level, vitamin A is non -negotiable for rhodopsin, which is the visual purple pigment you need for scotopic vision, meaning your ability to see in dim light.

It is also essential for synthesizing mucopolysaccharides and maintaining healthy mucus secretion.

When you understand those normal functions, the pathophysiology of a deficiency basically writes itself.

A lack of rhodopsin directly causes nictilopia.

Night blindness.

Night blindness, yes.

The patient literally cannot see when the lights go down.

Meanwhile, the lack of healthy mucus secretion causes the ectodermal tissues to dry out and undergo squamous metaplasia.

Clinically, you'll see diminished skin secretion, leading to follicular hyperkeratosis.

Basically, the hair follicles get plugged with keratin, creating these dry, horny papules, usually on the thighs and forearms.

And the eyes take a massive hit, too.

A devastating hit.

The conjunctiva and cornea become dry and wrinkled.

That's a condition called xerosis conjunctivae and xerophthalmia.

If you look closely at the eyes, you might see bitots spots.

Those are the white patches, right?

Elevated white patches made entirely of keratin debris right in the conjunctivae.

If this goes untreated, it progresses to keratomalacia, which means ulceration and scarring of the cornea and eventually irreversible blindness.

Deficiencies can also cause poor skull bone growth and a very specific anemia that will only respond to vitamin A therapy, not iron.

To confirm that in a lab, you test for low plasma vitamin A and low RBP, though you have to keep in mind that RBP drops during an acute phase inflammatory response or doing severe protein deficiency, so context matters.

Treatment is retinal palmitate.

But we should flip it to excess.

Yes, I had to read the section on acute vitamin A toxicity twice.

It actually cites cases from the Arctic where people experience severe acute poisoning just from eating polar bear liver.

It's one of those unforgettable textbook details.

Polar bear liver stores phenomenal toxic amounts of the vitamin.

In a more standard clinical setting, though, chronic excess causes fatigue, bone pain, hair loss, hepatomegaly, and benign intracranial hypertension.

And there's a huge warning for pregnancy.

A critical point for practice, yes.

Pregnant women are heavily advised to avoid eating liver entirely due to the teratogenic risk.

It can cause severe malformations in the fetus.

Also, keep in mind that drinking massive amounts of orange juice or eating pounds of carrots can cause keratinemia.

The patient's skin turns visibly orange, which looks terrifying and mimics jaundice.

It does, but your key lab differentiator is that their plasma bilirubin will be completely normal.

That brings us to vitamin D, calciferol.

The text notes this is primarily covered in the bone disorders chapter,

but regarding excess, an overdose causes severe hypercalcemia.

And because vitamin D is fat soluble and hides out in adipose tissue, that hypercalcemia can persist for weeks even after you stop the supplement.

Exactly.

The half -life is incredibly long.

Now, looking at vitamin E, alpha -tocopherol, it functions almost entirely as an antioxidant.

You usually only see a deficiency in conditions involving fat malabsorption, like cystic fibrosis, or in rare cases, a condition like

abetatopoproteinemia.

That's where patients lack low -density lipoprotein.

Right, LDL.

Since LDL is the carrier required to transport vitamin E, the vitamin just can't get to where it needs to go.

And without that antioxidant projection, the clinical result is increased red blood cell hemolysis.

In premature, low birth weight babies, it gets even more severe, causing retrolental fibroplasias in the eyes and dangerous interventricular hemorrhages in the brain.

In the lab, you measure this via plasma vitamin E levels, but it should ideally be expressed as a ratio of vitamin E to LDL cholesterol to get an accurate picture.

That's a great point.

The text also specifically notes that while vitamin E is a great antioxidant in theory,

massive clinical intervention trials supplementing it to protect against atherosclerosis have failed to show any real reduction in cardiovascular events.

Which is a great reminder that biochemical theory doesn't always perfectly translate to systemic therapy.

The last fat -soluble vitamin is vitamin K.

It is absolutely essential for the liver to synthesize prothrombin, along with coagulation factors A7, I, X, and X.

Interestingly, a significant portion of your daily requirement is actually synthesized by the helpful bacteria living in your helium.

Clinically, you'll administer vitamin K to reverse the effects of the anticoagulant warfarin.

You should highly suspect the deficiency if a patient has been on prolonged broad -spectrum antibiotics,

which carpet bomb that intestinal flora, or if they have fat malabsorption.

Here's where it gets really interesting.

Newborns are extremely vulnerable here.

They naturally have very low plasma vitamin K because it doesn't cross the placenta well.

On top of that, their little neonatal guts are completely sterile.

They haven't been colonized by those helpful vitamin -synthesizing bacteria yet.

It really is.

Because of this, they can develop hemorrhagic disease of the newborn, which usually presents with severe bleeding just two to three days after birth.

You test for this indirectly by looking at their coagulation specifically at prolonged prothrombin time or an elevated international normalize ratio, the INR.

That wraps up the fat soluble group.

Now we transition to the water soluble vitamins, the B complex and vitamin C.

Looking at the B vitamins as a family first, they generally function as enzyme cofactors.

If you picture the metabolic pathways in a cell, like in figure 15 .1, these vitamins are sitting right there driving the electron transfer chain and the formation of foods like grains and meats.

A clinical deficiency is rarely isolated to just one B vitamin.

It's usually a multiple deficiency, heavily tied to severe protein undernutrition.

Let's walk through them sequentially.

First is thiamine, B1.

Thiamine is a vital cofactor for the decarboxylation of two oxoacids.

Essentially, it's the key that allows pyruvate to convert into acetyl -CoA, which is a massive step in energy production.

Deficiencies are most often seen in chronic alcoholism.

You can also see it in populations eating large amounts of raw fish.

Because of the enzyme.

Right, raw fish contains thiaminase, an enzyme that literally destroys the thiamine in the gut.

The resulting clinical disease is berry -berry.

And we divide berry -berry into two distinct presentations.

Correct.

Dry berry -berry presents with severe neurological deficits,

sensory polyneuropathy, and a specific encephalopathy known as Wernicke -Korsakoff syndrome, which features confusion and memory loss.

Wet berry -berry, on the other hand, hits the cardiovascular system, characterized by massive peripheral edema and cardiac failure.

To confirm this in the lab, you don't measure the vitamin directly, you measure its function.

You look for reduced erythrocyte transketolase activity in the red blood cells.

Next is roboflavin, B2.

This one is incorporated into FMN and FAD.

Flavin mononucleotide and adenine dinucleotide.

The electron carriers.

Exactly.

They're reversible electron carriers that bounce around in biological oxidation systems.

If a patient lacks B2, they develop araboflavinosis.

The clinical picture is very visible.

Rough scaly skin, angular scleromatitis, where the corners of the mouth crack, chylosis, which are red, swollen lips, and a very distinct tender magenta -colored tongue.

In the lab, you test the red blood cells again, this time looking for a drop in the activity of the enzyme glutathione reductase.

Following roboflavin is nicotinamide.

Or niacin.

This forms NAD +, and NADP +, nicotinamide adenine dinucleotide.

These are the heavy lifters for oxidation reduction reactions.

A deficiency precipitates a brutal disease called pellagra.

The classic medical mnemonic for pellagra is the 3Ds, dementia, dermatitis, and diarrhea.

The dermatitis is highly photosensitive, appearing intensely on sun -exposed areas like the neck and arms.

But pellagra isn't always just a dietary lack, is it?

The text mentions a few internal metabolic traps.

Exactly.

Some nicotinic acid is normally synthesized endogenously from the amino acid tryptophan.

So if a patient has Hartnup's disease, which is a rare genetic defect in tryptophan transport, they can't absorb the building block, leading to a pellagra -like rash.

You also see this in carcinoid syndrome.

Right, where the tumor hijacks the tryptophan.

Yes.

The carcinoid tumor aggressively hijacks the body's tryptophan to synthesize massive amounts of 5 -hydroxy tryptamine, or serotonin, leaving nothing behind to make niacin.

The lab diagnosis for niacin deficiency involves looking for a low concentration of N -methyl nicotinamide in the urine.

Well, niacin issues often present with visible skin and GI symptoms.

If we look at pyridoxin, or B6, the clinical picture shifts more toward the blood.

B6 acts as a cofactor, mainly for transaminases.

A critical clinical pearl here involves the tuberculosis drug isoniazid.

That's a huge one to remember.

It structurally competes with pyridoxin in metabolic pathways.

Treating someone for TB can inadvertently plunge them into a B6 deficiency, leading to a rare sideroblastic anemia.

This is a confusing lab picture because it's a hypochromic microcytic anemia.

The red blood cells are small and pale, like an iron deficiency, but the patient actually has increased overloaded iron stores.

You confirm the B6 deficiency by giving an oral tryptophan load and measuring abnormally high amounts of xanthorhenic acid in the urine.

Moving to biotin and pantothenate.

Pantothenate is a foundational component of coenzyme A.

Biotin is a carboxylation cofactor.

Deficiencies are incredibly rare, but the text notes a fascinating dietary quirk for biotin.

I love this detail.

You can actually induce a severe biotin deficiency by eating massive amounts of raw egg whites.

The egg white contains a protein called avidin, which binds fiercely to biotin in the gut and completely prevents its absorption.

So bodybuilders drinking raw eggs take note.

A very specific hazard.

Now we arrive at a critically important pair, folate and vitamin B12.

Both are absolutely non -negotiable for the normal maturation of red blood cells.

Folate is crucial for transferring one -carbon units in DNA and RNA synthesis.

This mechanism is exactly why the cytotoxic chemotherapy drug methotrexate works.

It actively competes with folate to halt cell division.

And then there's vitamin B12, the cabalamans.

B12 absorption is a complex journey.

It requires intrinsic factor, a protein secreted by the parietal cells in your stomach.

The B12 binds to this intrinsic factor, travels the entire length of the small intestine, and is finally absorbed way down in the terminal ilium.

Let's look at the first case study from the chapter to see how this goes wrong in practice.

A 67 -year -old woman presents with deep tiredness, paresthesia or tingling in her feet, and a sensory peripheral neuropathy.

Her blood work shows a profoundly low B12 level of 90 nanograms per liter.

Her folate is completely normal.

Crucially, her mean corpuscular volume, or MCV, is elevated at 102 femtoliters.

That elevated MCV is the big red flag.

A normal red blood cell is usually in the 80 to 100 range.

At 102, she has macrocytosis.

Because her DNA synthesis is stalled without B12, the cells keep growing in size but can't divide properly, resulting in megaloblastic macrocytic anemia.

Fewer cells, but they are abnormally huge.

Furthermore, she tests strongly positive for parietal cell antibodies.

Which locks in the diagnosis of pernicious anemia.

Her own immune system is destroying her gastric parietal cells.

No parietal cells means no intrinsic factor, which means absolutely zero B12 absorption, no matter how much she eats.

To definitively prove this absorption defect, the lab runs the shelling test.

Walk us through how that test actually works.

You give the patient a very small oral dose of radiolabeled B12.

At the exact same time, you give them a massive non -radiolabeled intramuscular injection of B12.

This injection saturates the tissues, ensuring that if any of that oral radiolabeled B12 gets absorbed, it will instantly be flushed out into the urine.

In a patient with pernicious anemia, you won't find any radioactivity in the human because they absorb the oral dose.

But if you repeat the test and give them the radiolabeled B12 already bound to synthetic intrinsic factor and suddenly they do absorb it and excrete it in the urine, you have pinpointed the exact mechanical failure.

Now this is crucial.

Both folate deficiency and B12 deficiency cause the exact same megaloblastic anemia on a blood smear.

If a patient comes into the ER profoundly anemic, why can't we just give them a high dose of folate to fix the blood counts while we wait for the B12 labs to come back?

This raises an important question regarding patient management because doing that can cause irreversible neurological ruin.

If the patient is actually B12 deficient, administering folate will kickstart DNA synthesis and completely reverse the megaloblastic anemia.

Their blood counts will look great, but folate does absolutely nothing to protect the nervous system.

The B12 deficiency will quietly continue to ravage their spinal cord, severely aggravating a condition called subacute combined degeneration.

You must always confirm the diagnosis before treating.

The text also draws a direct line between these vitamins and cardiovascular health.

Specifically looking at figure 15 .2, both folate and B12, along with B6,

regulate the enzymes that break down homocysteine.

If you lack these vitamins, homocysteine builds up in the plasma.

Elevated homocysteine is a well -established independent factor for cardiovascular disease.

That brings us to our final water soluble vitamin, ascorbate, or vitamin C.

It acts as a powerful aqueous antioxidant and is structurally required for collagen synthesis.

Severe deficiency causes scurvy.

Because collagen maintains the structural integrity of blood vessels and tissues, you see fragility of vascular walls.

This leads to petechiae under the skin, poor wound healing, and famously, swollen spongy bleeding gums.

But the clinical detail here that really demands attention is the pediatric presentation.

Because collagen is essential for creating the bone matrix, children with scurvy have impaired bone formation right at the epidaeial -physiological junctions.

If you look at an x -ray of a scorbutic child, those bone junctions look visibly frayed and there is often superior steel bleeding.

It's one of those textbook details that keeps pediatricians up at night.

That specific pattern of bone damage and bleeding can so easily mimic non -accidental injury.

You have to actively rule out a simple ascorbate deficiency before making a devastating accusation of child abuse.

You can test for this with leukocyte or plasma ascorbate assays.

And as a quick note on excess, patients who take massive mega doses of vitamin C can end up increasing their oxalate levels, which precipitates into highly painful renal oxalate calculi or kidney stones.

Now we transition from the organic vitamins to the inorganic trace metals.

Let's start with zinc.

It acts as a co -factor for dozens of enzymes, notably polymerases and alkaline phosphatase.

A deficiency results in alopecia, poor wound healing, and dermatitis.

There's a rare autosomal recessive condition called aqua -dermatitis enteropathica, caused by a defect in the SLC39A4 gene, which encodes a specific zinc transporting protein.

One crucial lab pearl,

plasma zinc levels, drop significantly during acute phase inflammatory response.

Zinc binds primarily to albumin in the blood, and albumin itself is a negative acute phase reactant, meaning the body produces less of it when inflamed.

Less albumin means less measured zinc, even if total body stores are fine.

Next is copper.

It's a vital co -factor for cytochromes and is transported through the plasma by a protein called keruloplasmin.

A deficiency, as seen in the rare inborn error Manke's disease, gives the patient's hair a very characteristic kinky appearance.

But clinical biochemistry focuses heavily on cocker excess, presenting a fascinating case study in Figure 15 .3.

Yes.

Case 2 outlines a 21 -year -old man presenting with dysarthria, difficulty physically articulating speech, along with severe leg weakness and amino acids spilling into his urine.

His alanine transaminase, or ALT, is elevated at 98, indicating liver stress.

His carrier protein, keruloplasmin, is practically non -existent at 0 .08 grams per liter, and yet his urinary copper is sky high.

This is the classic tragic presentation of Wilson's disease.

There are two primary metabolic defects occurring simultaneously here.

First, his liver has impaired biliary excretion, meaning it can't dump excess copper into the bile, leading to massive copper deposition and liver cirrhosis.

Second, that genetic deficiency of keruloplasmin means there is very little carrier protein to safely hold the copper in the blood.

So while his total plasma copper might actually measure low, the amount of highly toxic, unbound free copper is incredibly high.

It spills out of the blood and deposits directly into the tissues.

And the tissue damage perfectly explains his symptoms.

The copper hits the basal ganglia in his brain, causing the dysarthria and leg weakness that hits the kidneys, causing renal tubular damage, which is why amino acids are leaking into his urine.

If you look closely at his eyes, you'll likely see the most famous clinical sign.

Kaiser Fleischer rings.

These are striking brownish green rings right at the outer edge of the cornea caused by copper depositing directly into decimus membranes.

To diagnose Wilson's definitively, you run the penicillamine test.

You give the patient an oral dose of penicillamine, which solubilizes the tissue copper.

If their urinary copper excretion suddenly shoots past 25 micromoles per day, you have your diagnosis.

You treat it long term with a chelating agent like D -Penicillamine to constantly pull that copper out.

Let's expand on the remaining trace metals as they each govern highly specific pathways.

Selenium mediates glutathione peroxidase, which is a major cellular antioxidant.

A severe deficiency, famously documented in certain selenium -poor soil regions of China,

causes Kaishen's disease, which is a fatal cardiomyopathy.

In clinical practice, selenium supplementation has also been shown to slow the progression of mild graves orbitopathy in thyroid patients.

Manganese serves as a cofactor for superoxide dismutase.

Interestingly, you mostly see manganese issues in excess, specifically in minors inhaling manganese ores.

It deposits in the basal ganglia and causes a severe Parkinson -like motor disease.

Chromium is an interesting one.

It acts strictly as a cofactor for insulin action.

Without adequate chromium, insulin signaling at the cellular receptor level becomes sluggish, mimicking insulin resistance.

Molybdenum is a necessary cofactor for xanthine oxidase, the enzyme responsible for breaking down purines into uric acid.

And cobalt is fundamentally essential because it sits at the exact structural center of vitamin B12.

The text notes a bizarre historical toxicity for cobalt.

Breweries used to use cobalt compounds as an additive to stabilize the foam in beer, which led to a spike in severe heart failure known as beer drinker's cardiomyopathy.

So what does this all mean?

We clearly need these minute inorganic metals to run our cellular machinery, but industrial or environmental exposure to heavy metals is extremely dangerous.

Exactly, which is why the chapter closes out with a look at metal poisoning.

Mercury toxicity, usually from inhaled vapors or ingested salts, presents with a distinct metallic taste in the mouth, followed by severe peripheral neuropathy and renal dysfunction.

Acute toxicity requires aggressive treatment with dimeric -aparol chelating agents, while chronic, low -level exposure might be managed with n -acetylpendicillamine.

Then there's aluminium toxicity.

You really only see this in patients with severe renal impairment.

Historically, before modern water purification, contamination of the massive amounts of water used in dialysis fluid caused devastating issues like dialysis dementia and a bone disease called renal osteodystrophy.

It is treated by infusing the chelator dysphyreoxam.

Finally, cadmium toxicity is primarily an occupational hazard seen in industrial workers exposed to fumes.

It selectively causes intense nephrotoxicity and subsequent bone disease.

Because it damages the renal tubules so specifically, clinicians monitor the extent of the damage by measuring raised concentrations of beta -2 microglobulin in the urine.

We have covered a tremendous amount of ground today.

From the core definitions of organic vitamins and inorganic trace elements, through the complexities of macrocytic anemias, all the way down to heavy metal chelation.

What this chapter really drives home is how routine clinical laboratory values, like a low transketolase assay, a high MCV, or a dropping caroloplasmin level, provide a direct real -time window into microscopic cellular pathways.

These tiny molecules dictate entirely how we diagnose and manage the patients sitting in front of us.

It's an incredible realization of how interconnected these systems are.

And before we close, consider this final thought.

We often treat our diet as simple caloric fuel, but based on everything we mapped out today, every meal is actually a daily dose of highly specialized biochemical software.

What happens when our modern highly processed diets subtly alter the availability of just one trace metal or one enzyme cofactor, not over days, but over decades?

Could this slow chronic software corruption be the invisible driver behind broader metabolic diseases we haven't even fully connected yet?

That is a profound question to carry with you as you move forward in your studies.

Thank you for joining us for this deep dive.

From the entire Last Minute Lecture team, we wish you the absolute best of luck on your clinical biochemistry exams.

You've got this.

Keep studying, and we'll see you next time.