Micronutrients: Vitamins & Minerals
Nutrition Fundamentals
Chapter 3 · Micronutrients: Vitamins & Minerals
Fat-Soluble vs. Water-Soluble
Fat-soluble vitamins — A, D, E, and K — accumulate in body tissue and carry a real toxicity risk from excess intake. Water-soluble vitamins — the B-complex vitamins and vitamin C — are generally safer, since the body excretes surplus amounts rather than storing them. This real distinction matters directly for how supplementation risk should actually be thought about later in this chapter.
Five Real, Classic Deficiency Diseases
Collagen fails to form properly, causing poor wound healing, bleeding gums, severe pain, and death — historically devastating on long sea voyages without fresh produce.
Reduced bone density and skeletal deformities in children.
Became endemic in East Asia after populations shifted to polished white rice; Wernicke encephalopathy and Korsakoff syndrome are real forms of it.
The real "four Ds": diarrhea, dermatitis, dementia, and death — tied to diets low in both niacin and the amino acid tryptophan.
Megaloblastic anemia and neurological damage — a genuine, real risk specifically for vegans, since B12 is found almost exclusively in animal-derived foods.
Real Risk Is Genuine — But Concentrated in Specific Groups
These five diseases are real and severe, but genuinely rare in well-nourished modern populations outside specific, identifiable risk groups — people with restricted diets, certain absorption disorders, or limited access to varied food. That distinction matters directly for the next section, which turns to a much larger population: people who are already generally well-nourished, but take a supplement anyway.
What the Real Evidence Says About Multivitamins
A 2019 meta-analysis in Annals of Internal Medicine, covering nearly 1 million participants, concluded that the vast majority of multivitamins had no significant effect on survival or heart attack risk. A 2024 study of 390,124 healthy adults found multivitamin use did not extend life expectancy. A 2018 meta-analysis stated plainly that conclusive evidence for benefit "across all dietary backgrounds was not demonstrated." The US Preventive Services Task Force's 2015 review found no clear evidence that multivitamins prevent cancer or heart disease, help people live longer, or make them healthier in any measurable way. The NIH's own Office of Dietary Supplements concluded that most research shows healthy people who take a multivitamin do not have a lower chance of diseases like cancer, heart disease, or diabetes.
When a Supplement Study Found Real Harm
The Honest Takeaway
Real deficiency in a specific vitamin or mineral is a genuine medical concern, worth taking seriously and addressing directly, especially in the specific risk groups named above. Blanket supplementation in someone already eating a varied, adequate diet is a genuinely different situation — the real, large-scale evidence doesn't support a general benefit, and in a few specific, well-documented cases, points to real harm instead.
Five Deficiency Diseases, at a Glance
| Disease | Missing Nutrient | Real Risk Group |
|---|---|---|
| Scurvy | Vitamin C | Historically, long voyages without fresh produce |
| Rickets | Vitamin D | Children with inadequate sun exposure/diet |
| Beriberi | Vitamin B1 | Diets centered on polished white rice |
| Pellagra | Vitamin B3 | Diets low in niacin and tryptophan |
| Pernicious Anemia | Vitamin B12 | Vegans, and certain absorption disorders |
Questions to Sit With
Beta-carotene supplementation was found to genuinely increase lung cancer risk in smokers specifically — not the general population. What does this real, group-specific finding say about the risk of applying one blanket supplement recommendation to everyone?
The real evidence against general multivitamin benefit comes from studies covering well over a million participants combined. Why do you think multivitamin use remains so widespread despite that scale of real, negative evidence?
Real deficiency diseases like scurvy and pellagra are genuinely severe, yet rare in specific risk groups today. How should a nutrition course honestly balance covering real historical severity against the real, current low likelihood of most readers actually encountering it?
Quick Reference — Chapter 3
- Fat-soluble vitamins (A, D, E, K) carry a real toxicity risk from excess; water-soluble vitamins (B-complex, C) are generally excreted when in surplus
- Five real, classic deficiency diseases: scurvy, rickets, beriberi, pellagra, and pernicious anemia
- Large real meta-analyses (2019, ~1 million participants; 2024, 390,124 adults) and the US Preventive Services Task Force all found no clear multivitamin benefit for cancer, heart disease, or lifespan in well-nourished people
- Real, documented harm exists in specific cases — beta-carotene increases lung cancer risk in smokers, and long-term vitamin E supplementation is linked to reduced life expectancy
- Real deficiency risk is genuine but concentrated in specific groups, not the general well-nourished population
What's Next
Chapter 4: Energy Balance: Calories, Metabolism & Weight Management.