September/October – 2004
by: Rob Santich MNHAA
Since its development from wild species, the lettuce in all its ingredient. It is thought that the first cultivated crop varieties has become the world’s most popular salad originated in or around the Mediterranean basin. The supporting evidence for this is the existence of a transitional, nearly wild species of lettuce. The morphology of this nearly wild species indicates that it originates from Lactuca serriola, commonly called pricking lettuce, in reference to the bristly stems and leaf margins. Cooking oil is extracted from the seeds of Lactuca serriola to this day, as it was in ancient Egypt. The second piece of compelling evidence is found in the tombs of the ancient Egyptians.
Archaeologists have discovered tomb paintings of bundles of prickly lettuce and these have been dated to be 4,500 years old1.
The first written records of lettuce cultivation and consumption was by the first ancient Greek historian, Herodotus. He recorded that lettuce appeared on the tables of the royal family of Persia in 550 BC. Lettuce was later described by various individuals:the ancient Greek physician and teacher of medicine, Hippocrates, in 430 BC described the sedative properties of the sap derived from the wild species as well as the health benefits of the cultivated variety; Aristotle, the ancient Greek teacher and philosopher, in 356 BC; and Galen, one of the most famous ancient Greek physicians and physiologists in 164 AD described lettuce as a popular salad vegetable1.
It appears as if lettuce was also popular in ancient Rome and several species had been developed and cultivated. Columella, a Roman writer on agriculture, described four species in 42 AD; and Pliny, the Roman author described nine varieties in 79 AD 1. The Roman Emperor Augustus attributed his recovery from serious illness to his treatment with wild lettuce. He was so impressed and thankful, he had erected an altar and a statue in honour of the plant 2.
In terms of the culinary variety, it was probably through the expansion of the Roman Empire that lettuce cultivation and consumption spread through northern and western Europe 1.
The cultivation of the Romaine or Cos lettuce spread through out the Mediterranean region, where to this day it remains the principle lettuce variety cultivated in southern Europe, the eastern Mediterranean coast and north Africa. The term Cos lettuce is highly suggestive of an early usage on the Greek Island of Kos. Leaf types and Latin lettuce were probably developed from the Romaine lettuce, as its morphology is similar but with shorter leaves and a softer texture. Butterhead is similar to Latin lettuce so it is likely that it was developed from it. The soft-headed crisp types, known as Batavia lettuces, were probably developed sometime later from leaf types that formed rudimentary heads under cool conditions 1.
Lettuce, along with other vegetables and fruits, was taken to the New World by the Italian explorer, Christopher Columbus. Peter Martyr d’Anghiera, a Spanish chronicler and historian who recorded the exploits of many Spanish explorers as well as Columbus, recorded the presence of lettuce on Isabella Island in the Caribbean in 1494, suggesting it arrived on Columbus’s second voyage of discovery 1.
During the early years of the Unites States, an assortment of cultivars and leaf types were grown, initially in home and farm gardens and later in market gardens around cities. During the early part of the 20th century, great developments in the shipping and transport industries allowed the expansion of new markets with increasing popularity.
It is likely that lettuce arrived in Australia with the first fleet, along with the unintentional delivery of many exotic weed seeds.
Two species of prickly lettuce grow wild in Australia, Lactuca serriola and L. saligna or willow leaf lettuce. Their distribution is wide, although L. saligna is not found in the Northern Territory. The plants are found as garden weeds, on roadsides and wasteland, as well as degraded pastures 3.
The Lactuca spp. are members of the family Compositae, sub-family Ligulifolae, and the order Campanulaceae. The Ligulifolia subfamily is characterized by the presence of latex vessels with the presence of essential oils a rarity. Other members include the common weeds with medicinal properties, Taraxacum officinale (Dandelion) and Cichorium intybus (Chicory) 4.
As lettuce growers and observant lettuce consumers are aware, all lettuce varieties exude a milky latex to varying degrees, mainly from the stem and leaf nodes when traumatised. The latex is particularly noticeable in stem varieties. It’s this latex that imparts a bitter taste to lettuce leaves, and of course is considered undesirable in commercial lettuce. However, this bitter latex has significant medicinal value. Throughout history, medical writers and physicians have recorded the health benefits of consuming lettuce as well as the medicinal properties of the milky latex. For example, Dioscorides, the ancient Greek military surgeon and naturalist, in his work De Materia medica, makes reference to the sedative properties of garden lettuce as well as the properties of the latex of the prickly lettuce, where he compares the sedative effect of the prickly lettuce to that of the opium poppy5.
In 1792, Dr Koxe, a medical doctor in Philadelphia, began to collect the milky latex from Lactuca sativa, dried it and prescribed the exudate as a substitute for opium. The news of this medicinal use soon spread through the medicinal community in the US and also to Europe. In Europe, the plant source of the latex was Lactuca virosa, but at that time in the US, Lactuca virosa had not introduced itself onto the landscape (Lactuca elongata, which grows wild in the US, seems to have been overlooked at this stage). As Lactuca virosa is a more abundant source of latex, Europe became the major producer of Lactucarium5.
Medicinal research on animals began in 1819 with Dr Ganzel of Berlin performing studies on dogs, noting that Lactucarium produced a profound sleep 5. Later in medical history, Lactucarium became an official drug of medicine and earned monographs in the Eclectic texts King’s American Dispensatory (1898), and The Eclectic Materia Medica, Pharmacology and Therapeutics by Harvey Wickes Felter MD (1922), as well as The British Pharmaceutical Codex (1911). These texts are still referred to in modern phytotherapy, as they represent credible traditional evidence for the use of herbs and are available on the internet in their entirety ([url]www. ibiblio.org[/url])
PHYTOCHEMISTRY OF THE LATEX FROM LACTUCA ssp.
Research into the identification of the phytochemicals present in lettuce latex began quite early in plant research history and this early research is thoroughly dealt with in reference ‘5’. More recently, with the development of sophisticated analytical equipment and methodologies, the phytochemistry of lettuce latex has been fully elucidated. The major constituents appear to be the sesquiterpene lactones, lactucin, deoxylactucin and lactucopicrin 6. Sesquiterpene lactones are pharmacologically active phytochemicals that also impart a bitter taste onto those plants they accumulate in. There are over 3,000 sesquiterpene lactones known and a good portion of them occur in the family Compositae and are considered a phytochemical characteristic of the family7. Other sesquiterpene lactones of interest are: artemisinin from Artemisia annua (Qing hao), which has antimalarial properties;and parthenolide from Tanacetum parthenium (Feverfew) with anti-inflammatory properties7.
Researchers have classified the sesquiterpene lactone group as phytoalexins, which form a part of the chemical defence network developed by plants and protect the plant from pathogenic attack 6,8. Sesquiterpene lactones are also known for producing contact allergic reactions7.
The sedative effect of wild lettuce has been attributed to the sesquiterpene lactones, lactucin and lactucopicrin 9, and in modern Phytotherapy is utilized principally in galenical extracts rather than extracts of the latex, and is prescribed to treat sleep disorders, restlessness, nervous excitability particularly in children, and irritable cough9.
VITAMIN K, LETTUCE AND OSTEOPOROSIS
The K vitamins, a group of napthoquinones, are required for the carboxylation of number of proteins, including the bone matrix protein osteocalcin10helping to strengthen the bone matrix. There is emerging evidence that suggests that vitamin K may have protective effects in terms of age related bone loss, and epidemiological evidence is suggestive of an association between low vitamin K intake and an increased risk of osteoporotic fracture risk 11.
Vitamin K occurs as a series of compounds with a common napthoquinone nucleus and differing isoprenoid side chains. The form that occurs in plants, phylloquinone or vitamin K1, is the major dietary source and is found in green leafy vegetables and certain vegetable oils, such as soybean, rapeseed and olive oils12. Vitamin K1 is associated with and most abundant in, photosynthetic tissues of plants;therefore, the greener the leaf, the higher the vitamin K1 levels13.
The most well-documented role of vitamin K is in the liver, where it acts as a cofactor in the coagulation cascade resulting in blood clotting. In fact, the “K” is derived from the German word “koagulation”14. Some people are at risk of forming blood clots, which can block the flow of blood in the arteries of the heart, brain or lungs resulting in heart attack, stroke or pulmonary embolism. These people may be prescribed anticoagulants such as warfarin, which inhibits coagulation through the antagonism of the action of vitamin K. Consequently, patients taking these drugs are cautioned against consuming large quantities of vitamin K containing foods in their diet15.
Vitamin K2, or menaquinone, is synthesized in the human gastrointestinal system by microflora and appear to be a minor portion of the daily requirement for vitamin K 12, 15. It appears as if approximately 60 to 70% of the intake of the vitamin K group is lost to the body through excretion, which emphasizes the requirement for a continuous dietary supply to maintain tissue reserves 12,1.
RECOMMENDED DAILY ALLOWANCE (RDA)
In Australia, there is uncertainty with regard to setting an RDA because of the variable production of vitamin K by bacteria in the colon. The requirement is believed to be 1µg/kg body weight/day16. Nutritional texts in references to data from the USA, commonly state that the average American diet contains between 300 and 500mg of vitamin K per day, which far exceeds the 1µg/kg body weight/day requirement16. Presuming the Australian diet is approximately similar to the US, one could assume that people in both countries are unlikely to suffer vitamin K deficiency. However, reliable data on the vitamin K content of foods has demonstrated the vitamin K intake of many individuals fails to meet the 1µg/kg body weight/day requirement16. The evidence suggests that even the requirement of 1µg/kg body weight/day may not be enough for vitamin K to maximally carboxylate the bone matrix protein osteoclacin16.
Osteoporosis is a skeletal disorder in which bone strength is compromised, which results in an increased risk of fracture. Sustaining a hip fracture is one of the most serious consequences of osteoporosis17. Worldwide, almost 50% of women and 30% of men will suffer a fracture related to osteoporosis in their lifetime, and in Australia the estimated direct cost of osteoporosis related fractures is $800 million annually18.
The term osteoporosis means bone fragility and is synonymous with low bone density. Undoubtedly, osteoporosis is a multifactorial disorder with nutritional factors such as vitamin K, vitamin D and calcium intake being several factors contributing to an increased risk of fracture. Other factors include, but are not limited to, increasing age, female gender, oestrogen deficiency, smoking, metabolic diseases, such as hyperthyroidism, and the use of corticosteroids and anticonvulsants17.
LETTUCE AND HIP FRACTURE
Positive studies have taken place investigating the hypothesis that high intakes of vitamin K are associated with a lower risk of hip fracture in women. A prospective analysis within the Nurses’ Health Study cohort involving 72,000 middle-aged and older women and taken over 10 years, concluded that low intakes of vitamin K is associated with an increased risk of hip fracture. Within this study the researchers took a closer examination of iceberg and romaine lettuce, spinach and broccoli, as these were the greatest dietary contributors to the vitamin K intake in this cohort. The researcher examined whether these foods had protective effects against hip fracture in a similar manner to that observed for vitamin K intake. Women who consumed lettuce one or more times a day had a 45% lower risk of hip fracture than women who consumed lettuce one or fewer times per week. There was no observed association with spinach or broccoli, although this may have been due to the lower frequency of consumption of these foods19.
VITAMIN K AND BONE MINERAL DENSITY (BMD)
The Framingham Offspring Study is a longitudinal, community based study of cardiovascular disease among the children and spouses of the participants in the original Framingham Heart Study cohort. Between 1996 and 2000, there were 3,532 participants in the sixth examination cycle of the study. The data examined from this cycle found higher vitamin K intakes were associated with higher bone mineral density (BMD) measurements20.
Numerous clinical studies have demonstrated that the supplementation of vitamin K alone or with other vitamins or minerals increases carboxylation of osteocalcin in post menopausal women with osteoporosis21, reduces serum undercarboxylated osteocalcin in elderly women with osteoporosis22, increases BMD in post-menopausal women with osteoporosis 23, and has a protective effect on prednisolone-induced loss of bone mineral density24.
Green leafy vegetables (GLV) offer an inexpensive source of antioxidant phytochemicals. In a study examining the antioxidant potential of 30 GLV, concluded that lettuce, omum and radish leaves demonstrated the highest values25.
It appears as if fresh lettuce is best in terms of antioxidant capacity when compared with lettuce stored under modified-atmosphere packaging (MAP) in studies performed on 11 healthy volunteers:the fresh lettuce demonstrated significantly greater antioxidant activity over lettuce stored under MAP26.
Lettuce has indeed moved from wild weed to functional food, and with adequate intake, seems to have some protective effect in terms of osteoporosis. As an enthusiastic neophyte home lettuce grower, I am encouraged by not only this research but what I’m producing from my own NFT unit. There is nothing like providing fresh lettuce leaves for the daily salad at family meal times. Now where did I leave my Lactucarium!
ABOUT THE AUTHOR
RobSantich MNHAA has over 20 years’ experience as a herbalist and medicine maker. Amember of the Complementary Medicines Evaluation Committee (CMEC) expert advisory panel, Rob is also Botanical Medicine faculty head at the Australian College of Natural Therapies and has served as an examiner on the board of the National Herbalists Association of Australia. He now runs a herbal practice in Newport, Sydney, and teaches classes in herbal manufacturing. Email: firstname.lastname@example.org
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