15.3 Dietary Supplements: Vitamins, Minerals, Amino Acids, Herbal, Homeopathic, and Hormonal Products
Key Takeaways
Under DSHEA (1994), supplements are regulated like foods: the FDA does not approve them before sale, and labels may make structure or function claims but not disease claims.
Fat-soluble vitamins A, D, E, and K can build up to toxic levels; vitamin K changes warfarin's effect, and high-dose vitamin E adds bleeding risk.
Long-term high-dose vitamin B6 can cause sensory neuropathy, and too much vitamin D causes high calcium with nausea, confusion, and kidney stones.
Potassium supplements with ACE inhibitors, ARBs, or spironolactone can cause dangerous hyperkalemia.
St. John's wort, SAMe, and 5-HTP can cause serotonin syndrome with antidepressants, and yohimbine raises blood pressure and heart rate.
15.3 Dietary Supplements: Vitamins, Minerals, Amino Acids, Herbal, Homeopathic, and Hormonal Products
Quick Answer: Supplements are 5% of the 2026 BIOM exam. The outline asks you to identify common supplements and their functions, recognize their side effects and interactions, identify clinically significant supplement-drug interactions, and recognize signs of abnormal levels. Know the fat-soluble vitamins (A, D, E, K) and their toxicities, the key minerals (calcium, magnesium, potassium, iron), and the listed products from amino acids to yohimbine. Herb-drug interactions involving Chinese herbs and botanicals are covered further in Section 15.4. The NIH Office of Dietary Supplements fact sheets are the outline's suggested reference.
How Supplements Are Regulated
- The Dietary Supplement Health and Education Act (DSHEA) of 1994 regulates supplements as a category of food, not as drugs.
- The FDA does not approve supplements for safety or effectiveness before they are sold. Manufacturers are responsible for safety, must follow good manufacturing practices, and must notify the FDA before selling a new dietary ingredient.
- Labels may make structure or function claims ("supports joint health") with a disclaimer that the FDA has not evaluated the statement, but not disease claims ("treats arthritis").
- Quality varies, and some products, especially sexual enhancement, weight loss, and bodybuilding products, have been found to contain hidden drugs. Third-party seals (such as USP or NSF) verify content and purity.
- Report serious adverse events to the FDA through MedWatch, and always record supplements in the medication history.
Vitamins
| Vitamin | Main roles | Deficiency | Excess and interactions |
|---|---|---|---|
| A (retinol) | Vision, immunity, skin | Night blindness, dry eyes | Headache, liver damage, bone loss; birth defects in pregnancy; beta-carotene supplements raise lung cancer risk in smokers |
| B1 (thiamine) | Energy metabolism, nerves | Beriberi; Wernicke encephalopathy (confusion, unsteady gait, abnormal eye movements) in alcohol use disorder | Very low toxicity |
| B2 (riboflavin) | Energy metabolism | Cracked lips, sore tongue | Harmless bright yellow urine; used for migraine prevention |
| B3 (niacin) | Energy metabolism, lipids | Pellagra: dermatitis, diarrhea, dementia | Flushing; high doses can harm the liver and raise blood sugar |
| B6 (pyridoxine) | Amino acid metabolism, nerves | Anemia, cracked lips, depression | Long-term high doses cause sensory neuropathy (numbness in the hands and feet) |
| B9 (folate) | DNA synthesis, red cells | Megaloblastic anemia; neural tube defects (400 mcg folic acid daily is advised before conception and in early pregnancy) | High folic acid can mask B12 deficiency |
| B12 (cobalamin) | Red cells, nerves | Megaloblastic anemia, numbness, balance and memory problems; risk with older age, vegan diets, metformin, PPIs, and gastric bypass | Very low toxicity |
| C (ascorbic acid) | Collagen, immunity, antioxidant | Scurvy: bleeding gums, easy bruising, poor wound healing | Diarrhea, kidney stones; increases iron absorption |
| D | Calcium absorption, bone, immunity | Rickets (children), osteomalacia (adults), osteoporosis | High calcium: nausea, constipation, confusion, kidney stones; the adult upper limit is 4,000 IU daily |
| E | Antioxidant | Rare; nerve and muscle damage | Bleeding risk at high doses, especially with anticoagulants |
| K | Clotting factors, bone | Bleeding; newborns receive a vitamin K injection | Reduces warfarin's effect: patients on warfarin should keep vitamin K intake consistent |
Minerals
| Mineral | Uses | Low levels | Excess and interactions |
|---|---|---|---|
| Calcium | Bone health | Muscle cramps, tingling, osteoporosis | Constipation, kidney stones; binds levothyroxine, tetracyclines, fluoroquinolones, and bisphosphonates, so separate the doses |
| Magnesium | Muscle cramps, constipation, migraine, sleep | Cramps, tremor, arrhythmias | Diarrhea; toxicity in kidney failure (weakness, low blood pressure, slow heart rate) |
| Potassium | Replacement during diuretic therapy | Weakness, cramps, arrhythmias | Hyperkalemia (weakness, dangerous arrhythmias) with ACE inhibitors, ARBs, spironolactone, or kidney disease |
| Iron | Iron deficiency anemia | Fatigue, pallor, brittle nails | Constipation, black stools, nausea; overdose can be fatal in children; avoid in hemochromatosis; absorption is reduced by calcium, tea, and acid reducers |
| Selenium | Antioxidant, thyroid function | Rare | Selenosis: garlic breath, hair loss, brittle nails |
Other Supplements on the Outline
| Group | Supplement | Common use | Side effects and interactions |
|---|---|---|---|
| Amino acids | L-glutamine | Gut health, recovery; a prescription form treats sickle cell disease | Generally well tolerated |
| L-lysine | Preventing cold sore recurrences | GI upset; evidence is mixed | |
| Choline | Liver and brain health, pregnancy | High doses cause a fishy body odor and low blood pressure | |
| Anabolic | Creatine | Strength and high-intensity exercise | Water retention and weight gain; raises blood creatinine without kidney damage, but use caution in kidney disease |
| Antioxidants | Coenzyme Q10 | Statin muscle aches (evidence mixed), heart failure, migraine | May reduce warfarin's effect; may lower blood pressure |
| Bone and joint | Glucosamine, collagen | Osteoarthritis, skin and joints | Glucosamine is often made from shellfish (allergy) and may raise the INR with warfarin |
| Digestive support | Digestive enzymes, probiotics | Lactose intolerance, antibiotic-associated diarrhea | Gas and bloating; probiotics rarely cause bloodstream infections in immunocompromised or critically ill patients |
| Energy support | Ashwagandha | Stress, sleep | Drowsiness, GI upset, rare liver injury; may raise thyroid hormone levels; avoid in pregnancy |
| Guarana | Energy, weight loss | A concentrated caffeine source: insomnia, palpitations, raised blood pressure | |
| Essential fatty acids | Fish oil (omega-3) | Lowering triglycerides | Fishy aftertaste, loose stools; high doses may modestly increase bleeding risk with anticoagulants and raise atrial fibrillation risk |
| Herbal | Saw palmetto | Urinary symptoms of BPH (large trials show little benefit) | Mild GI upset, headache |
| Valerian | Insomnia, anxiety | Drowsiness; adds to sedatives and alcohol | |
| Turmeric (curcumin) | Inflammation, joint pain | GI upset, rare liver injury; may increase bleeding risk with anticoagulants | |
| Homeopathic | Arnica | Bruising, muscle soreness | Highly diluted homeopathic products are generally safe; undiluted arnica is toxic if swallowed and should be used only on unbroken skin |
| Nux vomica | Indigestion, hangover | Made from seeds that contain strychnine; non-homeopathic preparations are poisonous | |
| Hormonal support | Melatonin | Sleep onset, jet lag | Drowsiness, headache; actual content often differs from the label |
| Wild yam | Marketed for menopause | Its diosgenin is not converted to progesterone in the body; evidence is lacking | |
| DHEA | Aging, libido, adrenal support | Acne, hair loss, excess hair growth, and voice deepening in women; avoid in hormone-sensitive cancers | |
| Mood support | St. John's wort | Mild to moderate depression | Induces liver enzymes (CYP3A4) and P-glycoprotein, reducing levels of birth control, warfarin, cyclosporine, HIV drugs, and digoxin; serotonin syndrome with antidepressants; sun sensitivity |
| SAMe | Depression, osteoarthritis | Can trigger mania in bipolar disorder; serotonin syndrome with antidepressants | |
| 5-HTP | Mood, sleep | Serotonin syndrome with SSRIs, SNRIs, MAOIs, triptans, or tramadol | |
| Sexual function | Yohimbine | Erectile dysfunction | Raises blood pressure and heart rate, anxiety, insomnia; dangerous with MAOIs, stimulants, and heart disease |
Recognizing Serotonin Syndrome
Serotonin syndrome can follow the combination of serotonergic supplements (St. John's wort, SAMe, 5-HTP) with prescription antidepressants, tramadol, triptans, or dextromethorphan. Signs include agitation, confusion, sweating, a fast heart rate, high blood pressure, fever, tremor, muscle twitching (clonus), and overactive reflexes, and diarrhea. Severe cases with high fever and rigidity are emergencies.
Practical Steps
- Ask every patient about all supplements, including teas, powders, and sports and weight-loss products.
- Check supplements against the patient's medications and conditions, especially anticoagulants, antidepressants, transplant and HIV drugs, birth control, diabetes drugs, and blood pressure medicines.
- Encourage patients to tell their physicians and pharmacists about supplements, and to stop those that affect bleeding before surgery as the surgeon directs.
- Stay within your state's scope of practice when recommending supplements.
A patient on warfarin has started a daily green smoothie with large amounts of kale and spinach and also takes a vitamin K supplement. What effect should the practitioner anticipate?
Increased bleeding, because vitamin K strengthens warfarin's anticoagulant effect
Serotonin syndrome
No interaction, because vitamin K is a supplement
Reduced anticoagulant effect (lower INR), because vitamin K counteracts warfarin
A patient who has taken 500 mg of vitamin B6 daily for two years reports numbness and tingling in both feet and hands. What is the most likely cause?
Vitamin B6 deficiency from poor absorption of the supplement
Sensory neuropathy from long-term high-dose vitamin B6
Vitamin C toxicity from a multivitamin taken alongside it
Calcium deficiency
A patient taking sertraline wants to add 5-HTP for low mood. What is the main concern?
5-HTP lowers blood sugar to dangerous levels
Combining 5-HTP with an SSRI can cause serotonin syndrome
5-HTP causes vitamin K deficiency and easy bruising
There is no concern because 5-HTP is a natural, plant-derived product
Which statement about the regulation of dietary supplements in the United States is accurate?
Under DSHEA, supplements are regulated as foods and may make structure or function claims but not disease claims
The FDA must approve each supplement's safety and effectiveness before it can be sold in stores
Supplements may legally claim to cure diseases as long as a disclaimer is printed on the label
Supplements are regulated exactly like prescription drugs and require large clinical trials and FDA approval before any sale
Sections you finish are checked off in the contents.