Most people are not deficient in most things — but specific vitamins and minerals are widely under-consumed, and a few supplements are genuinely worth taking. These guides separate the deficiencies that show up in real blood tests from the ones that show up in marketing copy, with research-backed dosing for each.
Muscle cramps, poor sleep, anxiety, and headaches can all be signs of low magnesium. Here's how to spot deficiency, who's most at risk, and how to fix it.
Read: signs you are low in magnesium →Fatigue, low mood, bone pain, frequent illness - these are all signs of vitamin D deficiency. Here's how to spot it and what to actually do about it.
Read: vitamin D deficiency symptoms →Vegans need to supplement B12 — there are no reliable plant sources. Here's the best form, the right dose, and the top products based on evidence and quality.
Read: best B12 supplement for vegans →Most iron supplements cause constipation and nausea. Gentler forms exist — and they work just as well. Here's what the research supports and the best products to buy.
Read: best iron supplement that won't cause constipation →Not all magnesium supplements work for sleep. We ranked the best forms and products based on research, bioavailability, and what the evidence actually supports.
Read: best magnesium supplement for sleep →The omega-3 supplement market is full of low-dose, rancid, or misleadingly labelled products. Here's what to look for and the best products that actually deliver EPA and DHA.
Read: best omega-3 supplement →The best vitamin D supplements for 2026 — what form to take, how much, D3 vs D2, with or without K2, and which products are worth buying.
Read: best vitamin D supplement →The vitamins and minerals with the strongest evidence for immune function — vitamin D, C, zinc, and more. What's worth taking and what isn't.
Read: best vitamins for immune system →Fish oil and algae oil both provide EPA and DHA omega-3s. One is animal-derived, one plant-sourced. Here's how they compare on evidence, purity, sustainability, and value.
Read: fish oil vs algae omega-3 →Folate and folic acid are both vitamin B9, but they're not identical. Here's what makes them different, which is better absorbed, and why MTHFR gene variants matter.
Read: folate vs folic acid difference →Vitamin D dosing depends on your blood levels, sun exposure, age, and why you're supplementing. Here's what the research supports - from maintenance to correcting deficiency.
Read: how much vitamin D per day →AG1 costs $3+ per serving. Is it worth the price? We look at the ingredients, the research, the marketing claims, and whether you can do better for less.
Read: is AG1 worth it →Magnesium glycinate and magnesium citrate are two of the most popular forms. They absorb well but have different uses. Here's how to choose the right one for your goal.
Read: magnesium glycinate vs citrate →Vitamin D supplements come in two forms - D3 (cholecalciferol) and D2 (ergocalciferol). D3 raises blood levels more effectively in research. Here's the full comparison.
Read: vitamin D3 vs D2 →Most people don't need a full supplement stack. Here's what vitamins are worth taking daily based on your diet, age, and actual deficiency risk.
Read: what vitamins should I take daily →Vitamin B12 makes red blood cells, maintains nerves, and builds DNA. It's found almost exclusively in animal foods - here's why that matters and what deficiency looks like.
Read: what does vitamin B12 do →Biotin is a B vitamin essential for fat, carbohydrate, and protein metabolism. Learn what it does, where to get it, and whether supplements actually work.
Read: what is biotin →Vitamin D, magnesium, omega-3, B12 (especially in vegans and older adults), and iron (especially in menstruating women) are the deficiencies that show up most consistently in population data. The rest are usually well-covered by a varied diet.
For most people eating a reasonably varied diet, a daily multivitamin is unnecessary insurance — but it's not harmful, and it does fill small gaps. Targeted supplements (vitamin D in low-sun months, B12 if vegan, iron if deficient) are usually a better return than a generic multi.
The only reliable way is a blood test. Symptoms like fatigue, low mood, or muscle cramps overlap with too many causes to self-diagnose. Vitamin D, B12, iron, and ferritin are the four most worth testing if you're unsure.
For most vitamins and minerals, no — the molecule is the same. What matters is the form (e.g., methylcobalamin B12 over cyanocobalamin for some people, glycinate magnesium over oxide for absorption) and third-party testing for purity. Brand premiums beyond that are mostly marketing.
Yes, especially fat-soluble vitamins (A, D, E, K) which accumulate in the body, and minerals like iron and zinc. Stick to recommended doses unless a clinician has tested you and prescribed higher amounts. Water-soluble vitamins (B and C) are harder to overdose on but still have upper limits.