Garlic

Name: GARLIC
Class: Herb
Risk Factor: C

Fetal Risk Summary

Allium sativum L. (Family, Alliaceae), better known as garlic, is a perennial bulb used as a food flavoring. In much higher doses, the herb has been used for medicinal purposes since ancient times. The medicinal parts of garlic are the whole fresh bulb, the dried bulb, and the oil. Studies have demonstrated antibacterial, antimycotic, lipid-lowering, and platelet aggregation inhibition properties. Garlic may prolong bleeding and clotting time and enhance fibrinolytic activity. The average daily doses for medicinal indications are 4 g of fresh garlic, 8 mg of essential oil, or one or two fresh garlic cloves (1,2,3,4 and 5).

The primary chemical constituents of garlic are the alliins (alkylcysteine sulfoxides), in particular the odorless, colorless amino acid, allylliin (S-allyl-L-cysteine sulfoxide). This amino acid, which has no pharmacologic activity, is converted by the enzyme, allinase (released from neighboring vascular bundle sheath cells by cutting or crushing the bulb) to allicin (diallyl-disulphide-mono-S-oxide but also known as diallyl thiosulfinate responsible for the pungent characteristic garlic odor), a sulfur-containing volatile oil. The unstable allicin then undergoes further changes to two major products, diallyldisulphide (a predominant compound in garlic breath) and diallytrisulphide, and several minor products, cycloalliin, vinyl dithiins, ajoene (4,5,9, trithiadodeca-1,6,11-triene 9-oxide), and methylallyltrisulphide (1,2,3 and 4).

Depending on the method of preparation, commercial garlic products may vary widely in their content of allicin, especially those in oil (3). In some cases, no detectable levels of allicin were found. A 1992 study that evaluated 18 garlic preparations of the approximate 70 that were commercially available in Germany found that only five had an allicin content equivalent to 4 g of fresh garlic, the average daily dose required for therapeutic effects (3). The other 13 products were considered “expensive placebos” because they had no pharmacologic activity (3).

Korean garlic juice was administered to rats to investigate whether it would protect against embryotoxicity induced by maternal ingestion of methylmercuric chloride (6). Analysis of Korean garlic juice indicated that it contained several types of free amino acids, including (numbers in parentheses are the number of amino acids for each type) neutral (N=7), sulfur-containing (N=3), acidic (N=2), basic (N=2), imino acid (N=1), and aromatic acid (N=3) with a total content of approximately 55 mg/mL. The pregnant rats were given 20 mg of methylmercuric chloride on gestational day 7 and then treated with either 0.5 or 1.0 g/kg Korean garlic juice or saline. A fourth group of rats was not treated with mercury or garlic juice. Korean garlic juice was effective, in a dose-related manner, in preventing or reversing the toxicity of organic mercury in terms of increasing maternal and fetal body weights, increasing fetal survival, and decreasing mercury levels in the organs and blood of dams and fetuses (6). The investigators concluded that the effects of Korean garlic juice were most likely due to the thiol groups found on several of the amino acids that resulted in chelation of the mercury, thereby protecting essential maternal and fetal enzyme systems (6).

Some of the chemical components apparently cross the placenta of animals and humans. In fetal sheep, the taste system develops between 50 and 100 days after conception (8). To determine if garlic crosses the sheep placenta, sheep were administered 6 mL of Egyptian garlic oil by gavage on approximately day 110 of gestation (7). A sensory panel of 16 judges, selected because of demonstrated ability to detect dilute concentrations of garlic in water, were used to determine if the odor was present in allantoic and amniotic fluid, fetal blood, and maternal blood. Samples were drawn at 0, 50, 100, and 150 minutes after the maternal dose. Paired samples (treated and untreated) were presented to each judge. Garlic odor was detected in amniotic fluid at 100 and 150 minutes, and in allantoic fluid, fetal blood, and maternal blood at 50, 100, and 150 minutes. In a brief letter, one correspondent said the odor of garlic had been noted on the breath of some human newborns (8). In a 1995 study, a sensory panel of 13 judges, screened for normal olfactory function, smelled paired samples of amniotic fluid from 10 women (9). Forty-eight minutes before amniocentesis in the 2nd trimester, five of the women received capsules containing the essential oil of garlic and five received placebo capsules containing lactose. The odor of garlic was judged to be stronger in four of the five women who had ingested the capsules with garlic. Therefore, this study demonstrated that components of garlic were transferred across the placenta and altered the odor of amniotic fluid (9). Although the specific components of garlic in the amniotic fluid were not identified, allicin (diallyl thiosulfinate) and at least one of its degradation products (diallyldisulphide) were most likely present because these are responsible for the characteristic odor of garlic (see above).

Two brief reports by a group of investigators in London stated that garlic might have benefits in preventing preeclampsia and intrauterine growth retardation (IUGR) (10,11). In an in vitro experiment, the investigators added increasing concentrations of garlic extract to a homogenate of human placental villous tissue to demonstrate a dose-related increase in nitric oxide synthase (enzyme that produces nitric oxide) activity (10). Because both calcium-dependent and calcium-independent nitric oxide synthase activities are decreased in preeclampsia and IUGR, the researchers speculated that garlic may be beneficial in these vascular conditions. In the second study, also using human placental villous tissue, both garlic extract and perchloric acid-treated garlic extract (allicin-negative) were shown to have cyclooxygenase inhibitor activity similar that of aspirin (11).

In summary, ingestion of garlic as a food flavoring appears to be safe during pregnancy. The herb has been used since ancient times and its use is so common that it is doubtful it presents any risk to the embryo or fetus. Some components of garlic do cross the placenta to the fetus, as shown by detection of a garlic odor in the amniotic fluid and on the newborn's breath. The use of high-dose garlic during gestation is not common and apparently has not been reported. Moreover, the lack of standardization of therapeutic garlic preparations would make any such study suspect unless analysis of the chemical constituents of the actual product used in the study was also reported. The complete lack of data on the outcome of animal or human pregnancies after high-dose garlic does not allow any assessment of its fetal risk. At least one source considers the use of large amounts of garlic during pregnancy to be contraindicated because of the potential for inducing menstruation or uterine contractions (5).

Breast Feeding Summary

At least some garlic constituents are excreted into breast milk. A 1994 study in lactating mice evaluated the effects on xenobiotic metabolizing enzymes in mouse pups from garlic administered to the mother (12). The lactating mice received either 200 or 400 mg/kg of crushed fresh garlic diluted in a volume of 0.1 mL of water for 14 or 21 days postpartum. Significant hepatic enzyme changes were measured in both the dams and pups, but the clinical significance of the changes is unknown.

Eight women, all exclusively breast-feeding their 3- to 4-month old infants, were the subject of a study published in 1991 examining the effect of garlic on the odor of breast milk and the nursling's behavior (13). None of the women was a regular user of garlic and their consumption of other sulfur-containing foods was limited before and during the study. In addition to breast feeding, milk samples were also collected from the women every hour for 4 hours. They were given either placebo or garlic (1.5 g of garlic extract) capsules on alternate days. A sensory panel of 11 judges, all screened for normal olfactory function, were able to consistently detect the odor of garlic from paired samples of expressed milk (treated and untreated) with a peak effect at 2 hours. It also appeared that the nursing infants detected the garlic odor because when the mother had ingested garlic capsules, the infants attached to the breast for significantly longer periods of time and sucked more. Although not significant, the infants also tended to consume more milk, but consumption may have been limited by the amount of milk available to the infant (13). A subsequent study confirmed that infants attached to the breast longer than usual when their mothers started taking garlic but that this effect disappeared with continued garlic ingestion (14).

The clinical significance of the above investigations is unknown. A review on the effect of various flavors in milk concluded that it was not known whether flavors such as garlic in milk had any effect on the subsequent development of food habits or willingness to accept new foods at weaning or later in life (15).

In summary, garlic ingestion by a lactating woman may impart garlic odor to her milk. The clinical significance of occasional garlic odor in milk appears to relate only to the amount of time the infant will be attached to the breast and this effect will disappear if the mother ingests the herb frequently.

References

  1. Allium Sativum. Garlic. PDR for Herbal Medicines, Montvale, NJ:Medical Economics, 1998:626–8.
  2. Garlic. Blumenthal M, Senior Editor. The Complete German Commission E Monographs. Therapeutic Guide to Herbal Medicines. Austin, TX:American Botanical Council, 1998:134.
  3. Robbers JE, Tyler VE. Tyler's Herbs of Choice. The Therapeutic Use of Phytomedicinals. Binghamton, NY:Haworth Press, 2000:132–7.
  4. Garlic. The Lawrence Review of Natural Products. St. Louis, MO:Facts and Comparisons, April, 1994.
  5. Garlic. Natural Medicines Comprehensive Database. Stockton, CA:Therapeutic Research Faculty, 1999:366–8.
  6. Lee JH, Kang HS, Roh J. Protective effects of garlic juice against embryotoxicity of methylmercuric chloride administered to pregnant Fischer 344 rats. Yonsei Med J 1999;40:483–9.
  7. Nolte DL, Provenza FD, Callan R, Panter KE. Garlic in the ovine fetal environment. Physiol Behav 1992;52:1091–3.
  8. Snell SB. Garlic on the baby's breath. Lancet 1973;2:43.
  9. Mennella JA, Johnson A, Beauchamp GK. Garlic ingestion by pregnant women alters the odor of amniotic fluid. Chem Senses 1995;20:207–9.
  10. Das I, Khan NS, Sooranna SR. Nitric oxide synthase activation is a unique mechanism of garlic action. Biochem Soc Trans 1995;23:136S.
  11. Das I, Patel S, Sooranna SR. Effects of aspirin and garlic on cyclooxygenase-induced chemiluminescence in human term placenta. Biochem Soc Trans 1997;25:99S.
  12. Chhabra SK, Rao AR. Transmammary exposure of mouse pups to allium sativum (garlic) and its effect on the neonatal hepatic xenobiotic metabolizing enzymes of mice. Nutrition Res 1994;14:195–210.
  13. Mennella JA, Beauchamp GK. Maternal diet alters the sensory qualities of human milk and the nursling's behavior. Pediatrics 1991;88:737–44.
  14. Mennella JA, Beauchamp GK. The effects of repeated exposure to garlic-flavored milk on the nursling's behavior. Pediatr Res 1993;34:805–8.
  15. Mannella JA. Mother's milk: a medium for early flavor experiences. J Hum Lact 1995;11:39–45.

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