Table 1.

Summary of human biomarker studies

Author et al., year (reference)Study designPopulationCriteria for each group of tobacco user (baseline)DurationProducts testedMarkers assessedaResults
Cravo et al., 2016 (207)To evaluate the safety profile of an EVP (2.0% nicotine) in smokers of CCs switching to use the EVPHealthy subjects (n = 408) in UKEVP group (n = 306):
  • - CPD

  • 5–10 CPD: 36%

  • 11–20 CPD: 56%

  • 21–30 CPD: 8%

  • - FTND

  • Mild: 30%

  • Moderate: 57%

  • Severe: 13%

12 weeksEVP prototype developed by Fontem Ventures B.V.Urine biomarkers: NEQ, SPMA, 3HPMA and total NNAL, PG% change in week 12 from baseline: EVP vs. CC
  • - NEQ: -25% vs. -6%

  • - 3HPMA: -29% vs. 6%

  • - SPMA: -35% vs. 1%

  • - Total NNAL: -31% vs. 3%

  • - PG: 119% vs. -3%

EVP group: (n = 306):
  • - Mean age: 34

  • - Mean BMI: 26

  • - 55% males

CC group (n = 102):
  • - CPD

  • 5–10 CPD: 31%

  • 11–20 CPD: 62%

  • 21–30 CPD: 7%

  • - FTNDa

  • Mild: 29%

  • Moderate: 54%

  • Severe: 17%

A rechargeable battery (voltage range of 3.0–4.2 V), an atomizer and a capsule (small cartridge) containing e-liquid
CC group (n = 102):
  • - Mean age: 35

  • - Mean BMI: 25

  • - 57% males

The base components of the e-liquids: PG (70%–75% w/w), glycerol (18%–20% w/w) and water (5% w/w)
Goniewicz et al., 2017 (214)To evaluate effects of e-cigs on nicotine delivery and exposure to selected carcinogens and toxicants in a longitudinal study within subjects; observational studyHealthy subjects (n = 20) in Poland
  • - Age 18 or older

  • - 100% Caucasian

  • - 40% males

  • - Mean age: 31

  • - Current daily cigarette smokers (>5 CPD within the last 12 months)

  • - Years of smoked: 12

2 weeksAn e-cig (M201 Mild, Poland) with 20 tobacco-flavored cartridges per week containing 11 mg of nicotine in a mixture of PGa and Glya (50:50)Urine biomarkers: NEQ, NNAL, Volatile organics: HEMA, MHBMA, HPMMA, 33HPMA, SPMA, AAMA, CNEMA, and 2HPMABaseline/Week 1/Week 2, P-value
  • - NEQ (μmol/g): 50/45/43, NS

  • - NNAL (ng/g): 165/60/69, <0.001

  • - HEMA (ng/g): 3120/864/1573, 0.001

  • - MHBMA (ng/g):: 1283/478/887, <.001

  • - HPMMA (μg/g): 1379/387/575, <.001

  • - 3HPMA (μg/g): 700/455/465, 0.001

  • - SPMA (ng/g): 674/193/481, <.001

  • - AAMA (μg/g): 148/188/97, 0.005

  • - CNEMA (μg/g): 178/58/66, <.001

  • - 2HPMA (μg/g): 24/18/15, <.001

  • - 1-Hydroxyfluorene (ng/g): 864/492/833, <.001

  • - 3-,4-Hydroxyphenanthrenes (ng/g): 669/544/1262, NS

  • - 2-Hydroxyfluorene (ng/g): 463/315/495, 0.048

  • - 1-Hydroxypyrene (ng/g): 338/279/627, NS

  • - 3-Hydroxyfluorene (ng/g): 312/192/349, 0.001

  • - 2-Hydroxyphenanthrene (ng/g): 333/492/800, NS

  • - 1-Hydroxyphenanthrene (ng/g): 211/196/415, NS

  • - 2-Naphthol (μg/g): 13/8/14, NS

Metabolites of PAHs (free plus conjugated): 2-naphthol, 1-hydroxyfluorene, 2-hydroxyfluorene, 3-hydroxyfluorene, 1-hydroxyphenanthrene, 2-hydroxyphenanthrene, 3+4-hydroxyphenanthrene; 1-hydroxypyrene
McRobbie et al., 2015 (215)To investigate exposure to nicotine and to acrolein before and after e-cigs useAdult smokers (n = 40) in UKE-cigs use only
  • - Mean CPD: 16

  • - Mean FTCD: 3.9

4 weeksA Green Smoke EC (labeled 2.4% nicotine)Urine biomarkers: 3-HPMA and cotinine% reduction in week 4 from baseline: E-cigs use only vs. dual users
  • - Cotinine (ng/mg creatinine): 17% vs. 44%, P = 0.010

  • - 3-HPMA (ng/mg creatinine): 79% vs. 60% P < 0.001

E-cigs use only (n = 16)
  • - Mean age: 45

  • - 63% white

  • - 50% males

Dual users
  • - Mean CPD: 21

  • - Mean FTCD: 4.7

Dual users (n = 17)
  • - Mean age: 48

  • - 53% white

  • - 52.9% males

Pulvers et al., 2016 (216)To assess nicotine consumption and toxicant exposure of cigarette smokers switching to e-cigs; observational study of smokers provided the e-cig independent of quitting intentionAdult US smokers (n = 40)Male (73%)4 weekse-Go C nonvariable battery and refillable atomizers and choice of eight flavors in 12 or 24 mg nicotine dosageUrine biomarkers: cotinine, NNAL, VOCsReductions (p value):
  • Cigs/day 50% (<0.001)

  • CO 37% (<0.001)

  • Cotinine 23% 0.(90)

  • NNAL 46% (<0.01)

  • PMA 17% (0.01)

  • HEMA 14% (0.85)

  • MMA increased 11% (0.27)

  • CNEMA 52% (<0.01)

  • 3-HPMA 21% (0.16)

  • 2-HPMA 12% (0.96)

  • AAMA 12% (0.67)

  • HPMMA 14% (0.99)

Mean age: 30.08 (SD = 8.82)
  • -White 50%

  • -Hispanic 25%

O'Connell et al., 2016 (217)D'Ruiz et al., 2016 (218)To compare changes in biomarkers among different user groups from usual brand conventional tobacco cigarettes to e-cigs and dual usesHealthy adult male or female smokers (n = 105) in USE-cigs use only
  • Group: A1/A2/A3

  • - CPD: 18/17/15

  • - Years smoked: 19/20/15

  • - FTND score: 5.3/5.1/5.3

5 daysBluTM e-cigsUrine biomarkers: NEQ, NNN, NNAL, 1OHP, 3HPMA, SPMA, MHBMA, HMPMA, CEMAE-cigs use only groups A1/A2/A3, Day -1 vs. Day 5 days
  • - NNAL (ng/24 h), 423/384/299 vs. 174/150/111

  • - 3HPMA (lg/24 h): 1522/1903/1354 vs. 214/263/247

  • - HMPMA (lg/24 h): 523/657/533 vs. 71/83/78

  • - CEMA (lg/24 h): 220/266/201 vs. 33/41/26

  • - 1OHP (ng/24 h): 317/302/261 vs. 94/86/91

  • - NNN (ng/24 h): 19/14/14 vs. 1/0.7/1

  • - MHBMA (lg/24 h): 5/6/5 vs. 0.3/0.3/0.3

  • - SPMA (lg/24 h): 6.3/8.1/6.3 vs. 0.3/0.3/0.4

  • - NEQ (mg/24 h): 17/18/15 vs. 11/13/11

E-cigs use only
  • - Group A1: Tobacco flavor rechargeable bluTM e-cigs

  • - Group A2: Cherry flavor rechargeable bluTM e-cigs

  • - Group A3: Cherry flavor disposable bluTM e-cigs

E-cigs use (n = 15 for each)
  • Group: A1/A2/A3

  • - Mean age: 37, 40, 33

  • - 87%, 60%, 93% white

  • - 60%, 80%, 40% males

Dual use
  • Group: B1/B2/B3

  • - CPD: 18/20/21

  • - Years smoked: 19/14/21

  • - FTND score: 5.5/5.7/5.2

All e-cigs contained 24 mg/mL (2.4%) nicotine, vegetable glycerol (∼50% in cherry flavor and ∼80% in tobacco flavor), PG (45% in cherry flavor and ∼10% in tobacco flavor), distilled water, and flavorings.Dual use groups B1/B2/B3, Day -1 vs. Day 5 days
  • - NNAL (ng/24 h), 431/422/343 vs. 329/321/269

  • - 3HPMA (lg/24 h): 1644/1475/1490 vs. 1046/1071/1155

  • - HMPMA (lg/24 h): 591/598/505 vs. 392/395/387

  • - CEMA (lg/24 h): 256/246/223 vs. 172/168/173

  • - 1OHP (ng/24 h): 364/295/304 vs. 235/206/224

  • - NNN (ng/24 h): 14/12/11 vs. 9/8/7

  • - MHBMA (lg/24 h): 5/3/5 vs. 4/3/4a

  • - SPMA (lg/24 h): 7/5/7 vs. 5/4/6

  • - NEQ (mg/24 h): 17/16/16 vs. 18a/16a/16a

Dual Use
  • - Group B1, B2, and B3: Usual brand combustible tobacco cigarette plus products from Group A1, A2, or A3, respectively.

Dual use (n = 15 for each)
  • Group: B1/B2/B3

  • - Mean age: 36, 36, 39

  • - 87%, 73%, 87% white

  • - 60%, 80%, 53% males

Note: All levels in Day 5 from three groups were statistically different compared to the levels in Day-1, a not significant.
Campagna et al., 2016 (219)To investigate long-term changes in exhaled breath measurements and respiratory symptoms in smokers invited to quit or reduce their cigarette consumption by switching to e-cigsRegular smokers not intending to quit (n = 134) in ItalyGroup A
  • - Packs/year: 25

  • - CPD: 20

  • - FTND: 5.5

  • - eCO: 18

  • - FeNO: 5.8

Baseline and at week 12, week 24, and week 52E-cig model ‘401’ with a rechargeable three-piece design
  • - There was no difference of baseline characteristics between failures, reduces, and quitters.

  • - A significant effect of quitting classification was found on FeNo and eCO at all time points (P < 0.0001).

  • - Among quitters, FeNO rose from 5.5 ppb to 17.7 ppb by week 52.

  • - Baseline eCO decreased from 17 ppm to 3 ppm by week 52.

  • - No significant changes in FeNO and eCO levels were observed in failures and reducers.

Group A: 12 weeks of Original either 2.4 mg/mL or 1.8 mg/mL nicotine)Group A (N = 49)
  • - Mean age: 45

  • - 26 males

Group B
  • - Packs/year: 24

  • - CPD: 18

  • - FTND: 5.6

  • - eCO: 21

  • - FeNO: 5.9

Group B: 6 weeks of Original either 2.4 mg/mL and a further 6 weeks of Categoria 1.8 mg/mL nicotine or no nicotineGroup B (N = 49)
  • - Mean age: 42

  • - 28 males

Group C
  • - Packs/year: 24

  • - CPD: 20

  • - FTND: 5.8

  • - eCO: 19

  • - FeNO: 6.4

Group C: 12 weeks of Original 0% without nicotine (sweet tobacco aroma)Group C (N = 40)
  • - Mean age: 40

  • - 25 males

Jorenby et al., 2017 (221)To evaluate, nicotine levels and smoking reduction success for cigarette smokers and dual users of cigarettes and e-cigsRegular smokers or dual users in USSmoker
  • - Years smoked: 25

  • - Mean FTCD: 4.9

26 days
  • - Disposable: 34%

  • - Replaceable cartridge: 16%

  • - Tank system: 14%

  • - Unknown: 37%

Urine biomarkers: Nicotine, CO
  • - Compared to smokers, dual users did not smoke significantly fewer cigarettes during either periods of ab libitum use or during periods of smoking restriction, nor did they produce lower CO levels.

Cigarettes only (n = 74)Smokers
  • - Mean age: 43

  • - 42% males

  • - 80% white

Dual users
  • - Years smoked: 17

  • - Mean FTCD: 4.5

Nicotine concentration
  • 0.1%–0.3%: 4%

  • 0.4%–0.6%: 8%

  • 0.7%–1.2%: 7%

  • 1.3%–1.8%: 8%

  • 1.9+%: 1%

  • Unspecified: 72%

Dual users increased vapes/day from 1.3 and 1.9during ad libitum use to 6.3 and 4.4 during 75% reduction for women and men, respectively.
Dual users: cigarettes + e-cigs (n = 74)Dual users
  • - Mean age: 33

  • - 41% males

  • - 91% white

Ad libitum period days 1–8 and 16–21
75% reduction period: Days 9–14
100% cessation period: Days 24–25
Vardavas et al., 2012 (223)To assess an impact of using an e-cigarette for 5 min on the pulmonary function tests and FENO of healthy adult smokersRegular healthy smokers (n = 40) in GreeceA minimum pack-year: 55 minNOBACCO MLB-MED filter, 11 mg of nicotine, PG>60%, linalool <5%, nicotine <10%, tobacco essence <5%, and methyl vanillin <1%; no polyaromatic hydrocarbons were detected.FeNOFeNO, ppb
  • - Experimental group

  • Pre usage: 13 vs. Post usage: 11, P = 0.005

Experimental group were instructed to use the e-cigs ad libitum for 5 min as they would usually smoke.Experimental group (n = 30) and control group (n = 10)
  • - Control group

  • Pre usage: 9 vs. post usage: 9, NS

The control group subjects were asked to use the e-cigarette with similar frequency, but without the e-cigs cartridge included.
Ferrari et al., 2015 (224)To compare the effects of ad libitum use of a nicotine free e-cigs or/and a cigarette for 5 min in healthy adult smokers (n = 10) and non-smokers (n = 10)Healthy subjects (n = 20) in ItalySmokers
  • - Packs/year: 19

5 min.ELIPS C SeriesFeNO and FeCOFeNO
  • Smokers: no difference, NS

  • Nonsmokers: no difference, NS

  • CO

  • Smokers: Decreased FeCO after e-cig use, P < 0.001

  • Nonsmokers: Decreased FeCO after e-cig use, P = 0.048

Smokers (n = 30)
  • - Mean age: 42

  • - 40% males

Non-smokers (n = 10)
  • - Mean age: 36

  • - 30% males

Schober et al., 2014 (225)To measure indoor air quality and FeNO levels of e-cig consumers9 healthy e-cig users in Germany
  • - 100% males

  • - Mean age: 25

All subjects were occasional smokers with a cigarette consumption of <10 cigarettes per week (no e-cigarettes)2 hoursLiquids (with and without nicotine, all with tobacco flavor) and rechargeable e-cigs from Red Kiwi, Seevetal, GermanyCO and FeNO
  • - FeNO increased in 7 of 9 individuals after vaping a nicotinic e-cigs at P = 0.030, but the effect was not significant when nicotine-free liquids were used.

  • - eCO levels were not significantly influenced by e-cig consumption.

In six vaping sessions, nine volunteers consumed e-cigs with and without nicotineNicotine: 18 mg/mL
  • aEVP, e-vapor product; CCs, conventional cigarettes; FTND, Fagerstrom test for nicotine dependence; Gly, glycerine; NEQ, nicotine equivalents; PG, propylene glycol; tobacco-specific nitrosamines, NNAL; volatile organic compounds: SPMA, 3HPMA HEMA, MHBMA, HPMMA, AAMA, CNEMA, and 2HPMA.