Table 2—

Biomarkers of nutrient intake most commonly used in clinical and epidemiological studies

Type of measurementBiological sampleLaboratory techniqueCommentsCharacteristics and sources[Ref.]
 CarotenoidsSerumHPLCPoor bioavailability in raw food, improved by mild cooking or heating (e.g. lycopene in tomato juice)Liposoluble143, 196–198
  β-CarotenePlasmaReflect short-term intakeRed, orange and yellow fruits and vegetables (sweet potato, carrots, winter squash)
  α-CaroteneInduced sputumNeed to control for cholesterol levelGreen vegetables
  LycopeneAdipose tissueAdipose tissue reflects long-term exposure
  LuteinMay not reflect concentration in target tissue
  Xanthine
  β-Cryptoxanthin
 TocopherolsSerumHPLCSerum and plasma reflect short-term intakeLiposoluble
  α-TocopherolPlasmaNeed to control for cholesterol levelVegetable and seed oils (corn, safflower, soy)143, 199
  γ-TocopherolAdipose tissueAdipose tissue reflects long-term exposureBeans, eggs, green vegetables
 Vitamin CSerumHPLCVitamin C in food can be destroyed by exposure to high temperature, oxidation or cooking in large amount of waterHydrosoluble
PlasmaResponse to intake up to 50–90 mg·day−1, then eliminated by renal clearance Reflects short-term intake Predicts intake at low level of vitamin intakeFruits: papaya, canteloupe, citrus fruits, strawberries Vegetables: cauliflower, broccoli, brussel sprouts, kale, sweet peppers143, 200
 SeleniumPlasmaAtomic absorption spectrophotometryAt higher levels of intake, the correlation between plasma selenium concentration and dietary intake depends on the chemical form of selenium in the dietCereals and grains143, 201–204
ToenailHPLCSelenium content of cereals and grains depends on the soil content Plasma reflects short-term intake Nail and whole blood reflect long-term exposure (>26–56 weeks)Animal products, especially organ meats and seafood
 FlavonoidsSerumHPLCMeasures the usual dietary intake over 1 weekApples, lemons, oranges205, 206
UrinePotatoes, cauliflower Tea Skin of tubers and roots Red wine
 IsoflavonoidsSerumGC/MSSex differences in metabolism and excretionLegumes: soybeans, beans, lentils, chickpeas.207–209
UrineHPLC
 LignansSerumHPLCSex differences in metabolism and excretionOil seeds (flax seed, soybean, rapeseed)
−24–72 h urineWhole-grain cereals (wheat, oats, rye), legumes, vegetables; fruits207–209
 PUFAFree fatty acids in serum or plasmaHPLCSamples are temperature and oxygen sensitiveFish oils210–212
 n-3 PUFAComponents of circulating triglyceridesGC/MSPotential for oxidation and degeneration over timeFish and shellfish
 n-6 PUFAPhospholipidsGLCFree fatty acids, phospholipids and cholesterol esters represent the intake over the last few days or mealsSoy and canola oil
Cholesterol esters
Red blood cell membranes EBC
Adipose tissueSerum fatty acids appear to be sensitive to changes in diet; high fluctuation (10–12%) and lab error <5% Components of triglycerides represent intake over the past few hours RBC reflect longer term intake (half-life of RBC: 120 days) RBC sample: collected whole blood is suspended in phosphate buffer and centrifuged; packed red cells are stored at −80°C RBC: may contain lower levels of n-3 and n-6 PUFA Adipose tissue reflects long-term intake if no severe weight loss has occurred
 FolateSerumELISASerum: short-term folateLeafy vegetables213, 214
RBCRBC: dietary intake over last 120 daysDry beans and peas, fortified cereal Some fruits
 ZincPlasmaAtomic absorption spectrometryPlasma: most frequently usedOysters202, 215–218
CellsPossibility of no association between zinc intake and plasma zincAnimal proteins
Erythrocyte, monocyte, neutrophil, plateletCells: complex sample preparationBeans
HairPoor sensitivity, imperfect specificityNuts
NailsPumpkin and sunflower seeds
Urine

  • HPLC: high performance liquid chromatography; GC: gas chromatography; MS: mass spectrometry; PUFA: polyunsaturated fatty acids; GLC: gas liquid chromatography; EBC: exhaled breath condensate; RBC: red blood cells.