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PubMed1984

The bronchodilator effects and pharmacokinetics of caffeine in asthma.

We compared the bronchodilator effects and pharmacokinetics of orally administered caffeine (10 mg per kilogram of body weight) and theophylline (5 mg per kilogram) in a double-blind, single-dose study in asthmatic patients 8 to 18 years of age. After 48 hours of withdrawal of all methylxanthines, 13 patients received caffeine and 10 received theophylline. Significant improvements in forced vital capacity, forced expiratory volume in one second, and forced expiratory flow rates occurred from one to six hours after administration of either caffeine or theophylline. The bronchodilator effect of caffeine did not differ significantly from that of theophylline and was maximal two hours after ingestion of each drug. Peak serum levels of caffeine (13.5 +/- 2.9 mg per liter) occurred at one hour, and peak levels of theophylline (8.4 +/- 1.7 mg per liter) at 2.2 +/- 0.8 hours. The mean serum half-time for caffeine was 3.9 +/- 1.4 hours and that for theophylline was 5.8 +/- 1.7 hours. All patients receiving caffeine metabolized it to paraxanthine, theobromine, and theophylline. Mild, transient side effects were seen after both caffeine and theophylline. Vital signs did not change significantly after either drug. We conclude that caffeine, a commonly available chemical, is an effective bronchodilator in young patients with asthma.

Adolescent↗
PubMed2003

Caffeine inhibits checkpoint responses without inhibiting the ataxia-telangiectasia-mutated (ATM) and ATM- and Rad3-related (ATR) protein kinases.

The ataxia-telangiectasia-mutated (ATM) and ATM- and Rad3-related (ATR) kinases regulate cell cycle checkpoints by phosphorylating multiple substrates including the CHK1 and -2 protein kinases and p53. Caffeine has been widely used to study ATM and ATR signaling because it inhibits these kinases in vitro and overcomes cell cycle checkpoint responses in vivo. Thus, caffeine has been thought to overcome the checkpoint through its ability to prevent phosphorylation of ATM and ATR substrates. Surprisingly, I have found that multiple ATM-ATR substrates including CHK1 and -2 are hyperphosphorylated in cells treated with caffeine and genotoxic agents such as hydroxyurea or ionizing radiation. ATM autophosphorylation in cells is also increased when caffeine is used in combination with inhibitors of replication suggesting that ATM activity is not inhibited in vivo by caffeine. Furthermore, CHK1 hyperphosphorylation induced by caffeine in combination with hydroxyurea is ATR-dependent suggesting that ATR activity is stimulated by caffeine. Finally, the G2/M checkpoint in response to ionizing radiation or hydroxyurea is abrogated by caffeine treatment without a corresponding decrease in ATM-ATR-dependent signaling. This data suggests that although caffeine is an inhibitor of ATM-ATR kinase activity in vitro, it can block checkpoints without inhibiting ATM-ATR activation in vivo.

Ataxia Telangiectasia Mutated Proteins↗
PubMed1990

Prenatal effects of maternal caffeine intake and dietary high protein on mandibular development in fetal rats.

The purpose of the present study was to determine the effects of caffeine on the mandibles of newborn rats whose dams were given a normal diet (200 g protein/kg diet) compared with those given a high-protein diet (400 g protein/kg diet) during gestation. A total of twenty pregnant Sprague-Dawley rats were randomly divided into four groups of five each. Starting on day 7 of gestation, groups 1 and 2 were fed on control and high-protein diets respectively, and groups 3 and 4 were pair-fed with groups 1 and 2 respectively, but with caffeine added to their diets. The caffeine supplement was 20 mg/kg body-weight. At birth, pups were killed and various measurements of their mandibles were made. The mandibular weights, calcium contents, and alkaline (EC 3.1.3.1) and acid (EC 3.1.3.2) phosphatase activities of the group given the caffeine-supplemented control diet were significantly lower than those of the corresponding unsupplemented group. Alkaline and acid phosphatase activities, collagen synthesis and hydroxyproline contents of the caffeine-supplemented high-protein group were greater than those of the corresponding unsupplemented group, whereas Ca and protein contents of the caffeine-supplemented high-protein group were lower than those of the corresponding unsupplemented group. There were no significant differences in plasma caffeine levels for either dams or pups between the caffeine-supplemented control and high-protein groups. The effects of caffeine on the development of fetal mandibles are apparently modified by different levels of maternal dietary protein.

Acid Phosphatase↗
PubMed1998

Association of coffee, green tea, and caffeine intakes with serum concentrations of estradiol and sex hormone-binding globulin in premenopausal Japanese women.

Caffeine intake has been proposed to influence breast cancer risk. Its effect may be mediated by hormonal changes. The relationships between caffeine-containing beverages (coffee, green tea, black tea, oolong tea, and cola) and serum concentrations of estradiol and sex hormone-binding globulin were evaluated in 50 premenopausal Japanese women. Intakes of caffeine and caffeine-containing beverages were assessed by a semiquantitative food-frequency questionnaire. Blood samples were obtained from each woman on Days 11 and 22 of her menstrual cycle. High intakes of caffeinated coffee, green tea, and total caffeine were commonly correlated with increasing sex hormone-binding globulin on Days 11 and 22 of the cycle after controlling for potential confounders [Spearman correlation coefficients (r) ranged from 0.23 to 0.31]. Green tea but not caffeinated coffee intake was inversely correlated with estradiol on Day 11 of the cycle (r = -0.32, p = 0.04). Although the effect of caffeine cannot be distinguished from effects of coffee and green tea, consumption of caffeine-containing beverages appeared to favorably alter hormone levels associated with the risk of developing breast cancer.

Adult↗
PubMed2006

Caffeine induces apoptosis of human umbilical vein endothelial cells through the caspase-9 pathway.

Caffeine is known to modulate placental and fetal umbilical circulation. It is demonstrated that apoptosis of human umbilical vein endothelial cells (HUVECs) is associated with placental umbilical vascular diseases. The present study was conducted to investigate the effects of caffeine on apoptosis of HUVECs. Isolated HUVECs were cultured under serum-free conditions for 24 h, and then treated with graded concentrations of caffeine (30, 100 and 300 microM) for additional 24 h and 48 h. The number of viable HUVECs was determined by cell counting. Apoptotic HUVECs were assessed by Hoechst33342 dye staining. The expression of caspase-9, caspase-8, caspase-3 and poly(ADP-ribose) polymerase (PARP) was assessed by Western blot analysis. Caffeine induced a dose- and time-dependent decrease in the number of viable HUVECs. Caffeine at concentrations higher than 100 microM significantly increased the percentage of apoptotic HUVECs. Caffeine at concentrations higher than 100 microM significantly increased cleaved caspase-9, caspase-3 and PARP expression in HUVECs at 24-h treatment compared with untreated cultures, whereas 30 microM caffeine significantly increased only caspase-3 expression at 24 h. Caffeine did not affect cleaved caspase-8 expression at 48 h. These results suggest that high concentrations of caffeine inhibit cell growth of HUVECs and induce apoptosis through the caspase-9 pathway.

Apoptosis↗
PubMed2000

Caffeine augments proteinuria in puromycin-aminonucleoside nephrotic rats.

Several studies indicate that increased intrarenal adenosine concentrations may attenuate puromycin-aminonucleoside (PAN)-induced nephropathy in rats. The purpose of this study was to investigate the chronic effects of caffeine, a nonselective adenosine receptor antagonist, on renal function and structure in PAN-induced nephropathy. Animals were randomized to receive drinking water or 0.1% caffeine solution. PAN was administered in two doses to a subset from each group at 1 week (100 mg/kg, s.c.; Purom-1) and 15 wks (80 mg/kg, s.c.; Purom-2) after initiating caffeine treatment (PAN and CAFF-PAN groups). The remaining animals served as time controls (CON and CAFF groups). Renal excretory function was followed for 23 wks. Caffeine consumption significantly augmented PAN-induced proteinuria after both PAN injections (Purom-1 and Purom-2, p<0.05 and p<0.001 respectively; CAFF-PAN vs. PAN). In addition, caffeine potentiated the transient reduction in creatinine clearance (CrCl) induced by PAN. Caffeine consumption for 23 wks significantly reduced CrCl in conscious nephrotic animals (4.76 +/- 0.98 vs. 8.51 +/- 1.55 L/kg/day, CAFF-PAN vs. PAN). Seven days after both PAN injections, increased plasma renin activity was detected in animals that were consuming caffeine as compared with corresponding control groups (CAFF and CAFF + PAN vs CON and PAN, respectively). Eight weeks after the second injection of PAN, acute measures of renal hemodynamic and excretory function were compared in anesthetized animals and renal samples were analyzed for histological changes. In PAN-rats, caffeine treatment for 23 weeks significantly reduced inulin clearance (0.28 +/- 0.09 vs. 0.57 +/- 0.12 mL/min/gr kidney. CAFF-PAN vs PAN, p<0.05), tended to increase renal vascular resistance (59.0 +/- 9.5 vs. 42.9 +/- 5.5 mmHg/mL/min/gr kidney, CAFF-PAN vs. PAN, p < 0.06), potentiated the development of more severe tubulointerstitial damage (tubular atrophy, presence of proteinaceous material, tubular dilatation, interstitial inflammation, interstitial fibrosis), and tended to increase glomerulosclerosis. In conclusion, this study indicates that caffeine adversely affects renal function in PAN-nephrotic rats, and that this effect may be due, in part, to increased activity of the renin angiotensin system.

Animals↗
PubMed2004

Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss.

BACKGROUND: Caffeine ingestion decreases the insulin sensitivity index (ISI) for an oral-glucose-tolerance test (OGTT) and decreases insulin-induced glucose disposal in lean male subjects during a hyperinsulinemic clamp. OBJECTIVE: We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men before and after a nutrition and exercise intervention. DESIGN: Nine sedentary, obese [body mass index (in kg/m(2)): 34.0 +/- 1.0] men who had refrained from exercise and caffeine ingestion for 48 h underwent 2 oral-glucose-tolerance tests (OGTTs). The subjects randomly received caffeine (5 mg/kg) or placebo 1 h before each OGTT. After a 12-wk nutrition and exercise intervention, during which time the subjects avoided dietary caffeine, the OGTTs were repeated. RESULTS: The intervention resulted in decreases (P < or = 0.05) in body weight (8.5 +/- 1.5 kg), percentage body fat (2.8 +/- 0.7%), and fasting glucose, insulin, and proinsulin concentrations and increases in the ISI for the placebo OGTT (P < or = 0.05). Caffeine caused a greater (P < or = 0.05) OGTT insulin response and a lower (P < or = 0.05) ISI both before and after weight loss. The proinsulin-insulin ratio indicated that neither weight loss nor caffeine affected the nature of the beta cell secretion of insulin. CONCLUSIONS: A nutrition and exercise intervention improved, whereas caffeine ingestion impaired, insulin-glucose homeostasis in obese men. The results are consistent with previous findings that caffeine ingestion contributes to insulin resistance.

Administration, Oral↗
PubMed2001

Misclassification of exposure: coffee as a surrogate for caffeine intake.

This study was conducted to assess the effect of exposure misclassification when coffee is used as a surrogate measure of caffeine exposure. Subjects were randomly selected from the telephone directories of four regional municipalities in southern Ontario, CANADA: Data on daily caffeine intake from foods, beverages, and medications were collected from June to November 1995 through self-administered, mailed questionnaires from 481 men and women aged 30-75 years. Although coffee was the main source of caffeine, cross-tabulations of exposure to coffee by total caffeine intake showed that assessment of coffee alone severely underestimated caffeine intake by at least one exposure level. A hypothetical 10-fold increase in risk was completely obscured when only coffee was used to estimate total caffeine intake. The results of this study suggest that measuring coffee instead of caffeine intake may contribute to a lack of positive findings in studies of coffee as a risk factor for disease occurrence, if in fact caffeine is the exposure of interest. On the other hand, measurement of coffee, tea, and cola soft drink intake in the present study appeared to approximate caffeine intake sufficiently and not affect risk estimates adversely.

Adult↗
PubMed2003

Association of maternal caffeine consumption with decrements in fetal growth.

Whether caffeine consumption during pregnancy represents a fetal hazard remains uncertain. The authors report on a large prospective study designed to examine this question. In 1996-2000, 2,291 mothers with singleton livebirths in Connecticut and Massachusetts were evaluated after their first prenatal visit and were questioned about caffeine consumption and important confounding factors. Urine samples were provided to analyze urinary caffeine, cotinine, and creatinine levels. Mothers were followed throughout pregnancy to monitor changes in consumption. Pregnancy outcomes were obtained from medical records. Self-reports of caffeine consumption in the first and third trimesters were not associated with intrauterine growth retardation, low birth weight, or preterm delivery. For every 1 mg/g creatinine increase in urinary caffeine, risk of intrauterine growth retardation was essentially unchanged (odds ratio (OR) = 0.96, 95% confidence interval (CI): 0.85, 1.08). In contrast, a 0.005 mg/g creatinine increase in urinary cotinine significantly increased risk (OR = 1.003, 95% CI: 1.001, 1.005). Mean birth weight was reduced by reported caffeine consumption (-28 g per 100 mg of caffeine consumed daily, 95% CI: -0.10, -0.46, p = 0.001) but not mean gestational age. Decaffeinated coffee did not increase risk for any perinatal outcome. This small decrease in birth weight, observed for maternal caffeine consumption, is unlikely to be clinically important except for women consuming >/=600 mg of caffeine daily (approximately six 10-ounce (1 ounce = 28.3 g) cups of coffee).

Adult↗
PubMed1983

Effects of caffeine on pancreatic tumorigenesis by 4-hydroxyaminoquinoline 1-oxide in partially pancreatectomized rats.

The effects of caffeine on pancreatic tumorigenesis by 4-hydroxyaminoquinoline 1-oxide (4-HAQO) and on pancreatic DNA synthesis were studied in partially pancreatectomized male Wistar rats. 4-HAQO was injected i.v. as a single dose of 7 mg/kg body weight 3 days after partial pancreatectomy. Caffeine was injected s.c. every 12 h at the maximum tolerated dose (m.t.d.) of 120 mg/kg body weight, half the m.t.d., and one quarter the m.t.d. from 12 to 72 h before and 0 to 72, 72 to 132, and 0 to 132 h after 4-HAQO treatment. Post-treatment with caffeine from 0 to 132 h had a dose-dependent biphasic effect on pancreatic tumorigenesis: post-treatment with the m.t.d. of caffeine decreased the total number of nodules, whereas treatment with one quarter the m.t.d. of caffeine increased their number. Decrease in the number of nodules was also observed on post-treatment with the m.t.d. of caffeine from 0 to 72 or from 72 to 132 h. Pretreatment with the m.t.d. of caffeine had no significant effect on the number of nodules. Recovery of pancreatic DNA synthesis was slower after simultaneous treatment with the m.t.d. of caffeine and 4-HAQO than after treatment with 4-HAQO alone. The possible mechanism of the effect of caffeine on pancreatic tumorigenesis induced by 4-HAQO in rats is discussed.

4-Hydroxyaminoquinoline-1-oxide↗
PubMed2002

A prospective study of the effects of female and male caffeine consumption on the reproductive endpoints of IVF and gamete intra-Fallopian transfer.

BACKGROUND: This study evaluated the timing and amount of caffeine intake by women and men undergoing IVF and gamete intra-Fallopian transfer (GIFT) on oocyte retrieval, sperm parameters, fertilization, multiple gestations, miscarriage, and live births. METHODS: A prospective study of 221 couples was conducted in Southern California between 1993 and 1998. "Usual" caffeine intake during lifetime and 1 year prior to attempt, caffeine intake during the week of the initial clinic visit, as well as intake during the week of the procedure, was evaluated from beverages (coffee, soda, tea) and chocolates. RESULTS: Not achieving a live birth was significantly associated with "usual" female caffeine consumption [adjusted odds ratios (95% confidence intervals): 3.1 (1.1, 9.7) and 3.9 (1.3, 11.6) for intake of >2-50 and 50 mg/day, compared with 0-2 mg/day] and consumption during the week of the initial visit [2.9 (1.1, 7.5) and 3.8 (1.4, 10.7)] female compared with 0-2 mg/day, although caffeine use was low. Infant gestational age decreased by 3.8 (-6.9, -0.7) or 3.5 (-6.7, -0.3) weeks for women who consumed >50 mg/day of caffeine "usually" or during the week of the initial visit. The odds of having multiple gestations increased by 2.2 (1.1, 4.4) and 3.0 (1.2, 7.4) for men who increased their "usual" intake or intake during the week of the initial visit by an extra 100 mg/day. Caffeine intake was not significantly associated with other outcomes. CONCLUSIONS: This is the first IVF/GIFT study to report any effect of caffeine on live births, gestational age, and multiple gestations. If these findings are replicated, caffeine use should be minimized prior to and while undergoing IVF/GIFT.

Abortion, Spontaneous↗
PubMed1985

A study of caffeine consumption and symptoms; indigestion, palpitations, tremor, headache and insomnia.

In a cross-sectional study of 4558 Australians, it was found that the proportion of subjects reporting indigestion, palpitations, tremor, headache and insomnia increased significantly with mean caffeine intake. A multiple logistic regression model was used to show that the association between the prevalence of these symptoms and usual daily caffeine consumption remained significant in both males and females for palpitations, tremor, headache and insomnia after controlling for the potential confounding factors of age, adiposity, smoking, alcohol intake and occupation. Adiposity was strongly correlated with the prevalence of indigestion and the apparent association between caffeine and indigestion disappeared when adiposity was controlled for. According to the logistic model, the relative risk of experiencing symptoms for people consuming 240 mg of caffeine (approximately 4-5 cups of coffee or tea) per day (the population average) compared with caffeine abstainers is 1.6 for palpitations, 1.3 for tremor, 1.3 for headache, and 1.4 for insomnia in males and 1.7, 1.5, 1.2 and 1.4 respectively for females. Further logistic regression analysis indicated that the associations found between caffeine intake and symptoms did not depend on the source of caffeine. In general, coffee consumption has no significant effect over and above that attributable to its caffeine content. If these associations are causal, then approximately one quarter of the reported prevalence of palpitations, tremor, headache and insomnia is attributable to caffeine consumption in this study population.

Adult↗
PubMed2003

Caffeine content of specialty coffees.

Caffeine is the world's most widely consumed drug with its main source found in coffee. We evaluated the caffeine content of caffeinated and decaffeinated specialty coffee samples obtained from coffee shops. Caffeine was isolated from the coffee by liquid-liquid extraction and analyzed by gas chromatography with nitrogen-phosphorus detection. In this study, the coffees sold as decaffeinated were found to have caffeine concentrations less than 17.7 mg/dose. There was a wide range in caffeine content present in caffeinated coffees ranging from 58 to 259 mg/dose. The mean (SD) caffeine content of the brewed specialty coffees was 188 (36) mg for a 16-oz cup. Another notable find is the wide range of caffeine concentrations (259-564 mg/dose) in the same coffee beverage obtained from the same outlet on six consecutive days.

Caffeine↗
PubMed2004

Selective inhibition of the DNA-dependent protein kinase (DNA-PK) by the radiosensitizing agent caffeine.

Caffeine inhibits cell cycle checkpoints, sensitizes cells to ionizing radiation-induced cell killing and inhibits the protein kinase activity of two cell cycle checkpoint regulators, Ataxia-Telangiectasia mutated (ATM) and ATM- and Rad3-related (ATR). In contrast, caffeine has been reported to have little effect on the protein kinase activity of the DNA-dependent protein kinase (DNA-PK), which is essential for the repair of DNA double-strand breaks. Previously, we reported that DNA-PK phosphorylates Thr21 of the 32 kDa subunit of replication protein A (RPA32) in response to camptothecin. In this report we demonstrate that the camptothecin-induced phosphorylation of RPA32 on Thr21 is inhibited by 2 mM caffeine. In addition, we show that caffeine inhibits immunoprecipitated and purified DNA-PK, as well as DNA-PK in cell extracts, with an IC50 of 0.2-0.6 mM. Caffeine inhibited DNA-PK activity through a mixed non-competitive mechanism with respect to ATP. In contrast, 10-fold higher concentrations of caffeine were required to inhibit DNA-PK autophosphorylation in vitro and caffeine failed to inhibit DNA-PKcs dependent double-strand break repair in vivo. These data suggest that while DNA-PK does not appear to be the target of caffeine-induced radiosensitization, caffeine cannot be used to differentiate between ATM, ATR and DNA- PK-dependent substrate phosphorylation in vivo.

Animals↗
PubMed1996

Caffeine intake and endogenous sex steroid levels in postmenopausal women. The Rancho Bernardo Study.

Caffeine intake has been associated with risk of osteoporosis, breast cancer, endometriosis, and fibrocystic breast disease and has been hypothesized to exert its effects through alteration of endogenous hormone levels. This study examined the cross-sectional association of caffeine intake with endogenous androgens, estrogens, and sex hormone-binding globulin in 728 white postmenopausal women aged 42-90 years in the Rancho Bernardo community-based study in 1984-1987. Caffeine intake was inversely associated with age and waist/hip ratio and positively associated with alcohol consumption. Significant inverse associations were noted between caffeine intake and bioavailable testosterone, which persisted after adjustment for age, waist/hip ratio, body mass index, alcohol intake, cigarette smoking, and physical activity (r = -0.10, p = 0.02). At high doses (equivalent to more than 2 cups of coffee or four cans of caffeinated soda daily), caffeine intake was positively associated with plasma estrone before and after adjustment for confounders (r = 0.26, p = 0.05). Sex hormone-binding globulin levels were positively associated with increasing caffeine intake (adjusted r = 0.09, p = 0.03). The positive association of caffeine with estrone and its inverse association with bioavailable testosterone suggest that caffeine's reported association with several chronic conditions may be mediated by an effect on endogenous sex steroids.

Adult↗
PubMed1995

Case-control study of caffeinated beverages and preterm delivery.

Although many women reduce their caffeine consumption once they known they are pregnant, 70-80% of pregnant women still consume caffeine. To evaluate the relation between caffeine consumption and preterm delivery, a case-control study was conducted to identify all preterm (< 37 weeks gestation) infants born to women in selected North Carolina counties from September 1988 through April 1991. Randomly selected full-term, normal-weight livebirths (matched by race and hospital) served as controls. The study population consisted of 408 cases and 490 controls. Telephone interviews with participants assessed the consumption of caffeinated coffee, tea, cola soft drinks, and noncola caffeinated soft drinks, with caffeine consumption measured by the number of daily servings of each beverage and the total milligrams of caffeine. Third-trimester caffeine consumption from all beverages combined showed a nonsignificant inverse association with preterm delivery. Both first- and second-trimester consumption of 1-150 mg/day were associated with a modestly increased risk of preterm delivery, while no association was found at higher consumption levels. Overall, these results do not support an association between caffeinated beverage consumption and preterm delivery, as is true in most previous studies.

Adult↗
PubMed2004

Risk-taking behavior: effects of ethanol, caffeine, and basal sleepiness.

STUDY OBJECTIVES: This study examined the effects of ethanol, caffeine, and basal sleepiness on a laboratory measure of risk-taking behavior, the Stop Light Task. The aims were to determine whether sleepiness and ethanol degrade psychomotor speed and risky choice and whether caffeine attenuates these effects. DESIGN: Mixed design with participants chosen for basal level of sleepiness and each assessed under 4 conditions presented in a Latin-square crossover design. PARTICIPANTS: Thirteen healthy adult volunteers aged 21 to 35 years. INTERVENTIONS: Participants received ethanol 0.5 g/kg and caffeine placebo, ethanol 0.5 g/kg and caffeine 150 mg, ethanol 0.5 g/kg and caffeine 300 mg, or a dual (ethanol-caffeine) placebo between 9:00 am and 9:30 am. MEASUREMENTS: The Multiple Sleep Latency Test (MSLT) was used to determine basal level of sleepiness. Subjects completed the Stop Light Task about 60 to 90 minutes after drug administration to assess psychomotor speed and risky choices. RESULTS: Seven subjects were classified as Alert (MSLT = 12.6 +/- 2.0 minutes) and 6 Sleepy (MSLT = 8.1 +/- 1.0 minutes). Sleepy compared to Alert subjects did not differ in psychomotor speed overall. Ethanol significantly slowed psychomotor speed relative to placebo, and ethanol-caffeine combinations attenuated this effect. Consistent with previous studies using the Stop Light Task, higher response requirements (FR15-FR50) and higher point loss probability (12.5%, 37.5%, 100%) significantly decreased risky choice, across sleepiness and treatment conditions. Alert subjects made "go" (primary measure of risk-taking) choices more often at lower response requirements and less often at higher response requirements, relative to Sleepy subjects. Ethanol did not significantly affect "go" choices but did produce changes in "go" choices as a function of response requirement. Given their more optimal pattern of choice behavior, Alert subjects gained significantly more money than Sleepy subjects; ethanol and caffeine combinations did not significantly affect money earned. CONCLUSIONS: These data suggest that sleepiness moderates risky choice such that Alert subjects have improved choice "acuity." Also, under conditions where risk-taking depends on responding rapidly (like the Stop Light Task), ethanol may also impair responding and caffeine may attenuate this effect.

Adult↗
PubMed2006

Laboratory and field studies of naps and caffeine as practical countermeasures for sleep-wake problems associated with night work.

STUDY OBJECTIVES: To evaluate the effects of napping, caffeine, and napping plus caffeine on performance and alertness in both laboratory and field settings. DESIGN: (1) Laboratory Study: parallel-groups design with random assignment to 1 of 4 experimental conditions. (2) Field Study: crossover design. SETTING: Sleep laboratory and field settings. PARTICIPANTS: (1) Laboratory Study: 68 healthy individuals; (2) Field Study: 53 shiftworkers who worked nights or rotating shifts. INTERVENTIONS: (1) Laboratory Study: an evening nap opportunity before the first 2 of 4 consecutive simulated night shifts plus placebo taken all 4 nights, caffeine taken nightly, the combination of the nap and caffeine conditions, or placebo. (2) Field Study: an evening nap on the first 2 of 4 consecutive night shifts plus caffeine taken nightly versus placebo taken nightly without naps. MEASUREMENTS AND RESULTS: (1) Laboratory Study: Napping, caffeine, and their combination all improved alertness and performance as measured by Maintenance of Wakefulness Test and Psychomotor Vigilance Task, but the combination of napping and caffeine was best in improving alertness. (2) Field Study: Napping plus caffeine improved performance as measured by Psychomotor Vigilance Test and decreased subjective sleepiness in individuals working the night shift. CONCLUSIONS: Napping plus caffeine helps improve performance and alertness of night-shift workers.

Adolescent↗