Lemon (Citrus limon): A Comprehensive Scientific Review

Definition and Types

Lemon is a yellow, oval or elliptical, fleshy and juicy citrus fruit. The thick and porous skin surrounds the segments, which contain sour juice sacs and seeds inside. The characteristic sour taste of lemon is due to its high citric acid content.

There are many varieties of lemon, but the most common commercially are the following:

• Eureka Lemon It is a thick-skinned and juicy variety most commonly found in markets.
• Lisbon Lemon: It has thinner skin and fewer seeds.
• Meyer Lemon Thought to be a hybrid of mandarin and lemon, it is a sweeter and thinner-skinned variety with a light orange color.

Biochemical Composition

Lemon has a rich profile of bioactive compounds that underpin its potential effects:

• Vitamins
  • Vitamin C (Ascorbic Acid): It is the most prominent and most abundant vitamin of lemon. A powerful antioxidant, it is essential for immune system function, collagen synthesis, iron absorption and wound healing. One medium lemon (about 58 grams) can provide about half of the daily vitamin C requirement.
  • Folic Acid (Vitamin B9): It is important for cell division and growth and plays a role in the prevention of neural tube defects, especially during pregnancy.
  • Vitamins B2 (Riboflavin), B5 (Pantothenic Acid) and B6 (Pyridoxine): It is important for energy metabolism and nervous system function.
• Minerals It contains trace amounts of minerals such as potassium, calcium, magnesium and phosphorus. Potassium plays an important role in blood pressure regulation.
• Dietary Fiber: Lemon peel and pulp in particular contain soluble fibers such as pectin. Fiber supports digestive health and helps balance blood sugar and cholesterol levels.
• Organic Acids:
  • Citric Acid It is the main acid responsible for the sour taste of lemon and its concentration is very high (%5-8). Citrates play a role in preventing kidney stone formation.
• Phytochemicals (Bioactive Compounds):
  • Flavonoids It contains various flavonoids such as hesperidin, eriocitrin, diosmin, naringin. These compounds have antioxidant, anti-inflammatory and cardioprotective properties.
  • Limonoids Compounds such as limonin, nomilin, narangin contribute to the bitter taste of lemon and have potential anticancer effects.
  • Essential Oils The essential oil extracted from lemon peel contains D-limonene and terpenes such as citral, beta-pinene and gamma-terpinene. D-limonene is responsible for the characteristic odor of lemon and may have anti-inflammatory, antioxidant and potential anticancer properties.

Effects on Body Functions

Lemon's rich nutrient and bioactive component profile offers a wide range of efficacy:

1. Immune System: Lemon supports the immune system significantly thanks to its high vitamin C content. Vitamin C strengthens the body's resistance to infections by increasing the production and function of white blood cells (especially phagocytes and lymphocytes). Furthermore, as a powerful antioxidant, it protects immune cells from oxidative damage and can help reduce the duration and severity of colds.
   • Research Example: A review by Maggini et al. (2017) detailed the multifaceted positive effects of vitamin C on the immune system, including increased resistance to infections and protection of immune cells.
2. Antioxidant Effects: Lemons are rich in powerful antioxidants such as vitamin C, flavonoids and limonoids. These compounds neutralize oxidative stress caused by free radicals in the body. Oxidative stress plays an important role in the aging process and the development of many chronic diseases (cancer, heart disease, neurodegenerative diseases).
   • Research Example: A study by Li et al. (2014) demonstrated the potent antioxidant activities of lemon flavonoids and limonoids, emphasizing their ability to protect cells from oxidative damage.
3. Anti-inflammatory Effects: Bioactive compounds such as flavonoids (hesperidin, eriocitrin) and D-limonene found in lemon peel and juice exhibit anti-inflammatory properties by inhibiting the production of pro-inflammatory cytokines and enzymes (COX-2, iNOS). This may help reduce the risk of chronic inflammation-related diseases (arthritis, metabolic syndrome).
   • Research Example: An animal study by Assini et al. (2013) showed that lemon extracts and the flavonoids they contain suppress inflammatory responses.
4. Cardiovascular Health: Lemon offers important benefits for cardiovascular health:
   • Blood Pressure Regulation: The high potassium content and flavonoids can lower blood pressure by helping blood vessels relax.
   • Cholesterol Management: The soluble fiber (pectin) and flavonoids in lemons may help lower LDL (bad) cholesterol levels.
   • Vascular Health: With its antioxidant and anti-inflammatory effects, it improves vascular endothelial function and reduces the risk of atherosclerosis.
   • Research Example: Lemon flavonoids such as hesperidin have been shown to improve endothelial function and reduce vascular inflammation (Ghanim et al., 2011).
5. Kidney Stone Prevention: Lemon juice increases citrate levels in urine thanks to its high citric acid content. Citrate reduces the risk of kidney stone formation by preventing calcium from crystallizing in the urine. It is especially effective for calcium oxalate stones.
   • Research Example: A review by Worcester and Coe (2010) stated that citrate treatment is an effective strategy to prevent kidney stone recurrence and emphasized that lemon juice can be used for this purpose.
6. Digestive Health and Weight Management: The pectin fiber found in lemons may increase the feeling of fullness by slowing gastric emptying and thus help with weight management. Lemon juice can support stomach acid production by stimulating the digestive system.
   • Research Example: The positive effects of fiber intake on weight management are well documented (Slavin, 2013), and lemon fiber contributes to these effects.
7. Skin Health: The high vitamin C content is vital for collagen synthesis. Collagen is an essential protein that provides skin elasticity and firmness. Antioxidants protect the skin from oxidative damage caused by the sun and environmental factors, which can delay the signs of aging.
8. Anticancer Potential: Bioactive compounds such as flavonoids (especially naringin, hesperidin), limonoids and vitamin C contained in lemons have shown anticancer effects in laboratory and animal studies. These compounds can inhibit the growth of cancer cells, promote apoptosis (programmed cell death) and suppress metastasis.
   • Research Example: A review by Kumar et al. (2020) indicated that citrus limonoids have promising anticancer potential in various types of cancer (colon, breast, liver).
9. Increasing Iron Absorption: The high vitamin C content of lemon significantly increases the absorption of plant-derived (non-heme) iron. For people with or at risk of iron deficiency anemia, consuming lemons with iron-rich foods may be beneficial.
10. Physical Performance: Lemon can support hydration during exercise. Its vitamin C content may help muscle recovery as an antioxidant. However, there is limited scientific evidence for a specific direct physical performance-enhancing effect.
11. Reproductive Health: Lemons are important for reproductive health thanks to their folic acid (vitamin B9) content. Folic acid is essential for DNA synthesis and cell division and is critical for the prevention of neural tube defects, especially before and during early pregnancy. Vitamin C is also an antioxidant that can have positive effects on sperm quality and female reproductive health.

Areas of Use

Lemon has a wide range of uses:

• Kitchen: It is used to add sour flavor and freshness to dishes, salads, sauces, soups, desserts and beverages. It goes well with fish and seafood. The peel is grated and used as a flavoring.
• Drinks It is the main ingredient in drinks such as lemonade, iced tea, cocktails and detox waters. Adding sliced lemon to water can encourage water consumption.
• Food Storage: Lemon juice is used to prevent browning (oxidation) of fruits and vegetables.
• Cosmetics and Cleaning: Essential oil from lemon peel is used in perfumes, soaps and cleaning products. It can also be used in household cleaning as a natural disinfectant and deodorizer.
• Traditional Medicine: In some cultures it has been used for digestive problems, colds, coughs and skin problems.

Side Effects and Dosage Information

Lemons are generally considered safe and healthy in normal consumption quantities. However, side effects may occur with excessive consumption or in some special cases.

Side Effects:

• Tooth Erosion: Due to the high acid content of lemon (citric acid), frequent or excessive consumption can lead to erosion of tooth enamel. To reduce this risk, it is recommended to rinse the mouth with water or use a straw after drinking lemon juice.
• Acid Reflux / Heartburn: In people with sensitive stomachs or those with gastroesophageal reflux disease (GERD), consumption of lemon juice may cause heartburn, burning sensation or worsening of other symptoms.
• Skin Irritation (Topical): Lemon juice can cause irritation in some people when applied directly to the skin or phytophotodermatitis (a chemical reaction that causes redness and blisters on the skin) when exposed to the sun.
• Drug Interactions: Lemon juice, like other citrus fruits (especially grapefruit), may contain furanocoumarins, which can affect the metabolism of some medicines (e.g. statins, calcium channel blockers). However, the concentration of these compounds in lemons is generally lower than in grapefruit and there is less risk of interference. Nevertheless, people taking regular medication are advised to consult their doctor before excessive consumption of lemon juice.
• Allergies Rarely, in people with citrus allergies, lemon consumption can cause allergic reactions (itching in the mouth, swelling, skin rash, shortness of breath).

Dosage

Since lemon is a food, there is no specific "dosage". It is consumed as part of the daily diet.

• For General Health: The juice of half to one lemon a day (mixed in water or used in cooking) provides enough vitamin C and other beneficial compounds for most adults.
• Kidney Stone Prevention: To prevent kidney stone recurrence, 1/2 cup (about 120 ml) of diluted lemon juice daily is usually recommended, but this should be determined by a physician on an individual basis.

It is beneficial to use fresh lemon juice or rind as part of a balanced diet. It is important to consume in moderation and to be mindful of possible side effects.

Storage Conditions

Proper storage conditions are important to preserve the freshness and nutritional value of lemons:

• Room Temperature Whole, fresh lemons can last for about 1 week at room temperature (20-25°C) in a well-ventilated place out of direct sunlight.
• Refrigerator For longer storage, it should be stored in the crisper drawer of the refrigerator. It can keep its freshness in the refrigerator for up to 3-4 weeks.
• Open or Sliced Lemons: Cut or sliced lemons should be stored in the refrigerator, wrapped in airtight cling film or in a closed container. This way they can last for several days.
• Ice cream Lemon juice can be frozen in ice molds and used later. You can also freeze grated lemon peels in an airtight container. Whole lemons can also be frozen, but the texture may change slightly after thawing.

Conclusion and Future Research

Besides being a flavoring and refreshing element in our kitchens, lemon is a valuable citrus fruit with many potential areas of action thanks to its high levels of vitamin C, flavonoids, limonoids and bioactive compounds such as essential oils. Its immune system support, antioxidant, anti-inflammatory and cardiovascular protective effects, role in preventing kidney stone formation and potential anticancer properties make it an important part of a healthy diet. Potential side effects such as tooth erosion and stomach upsets that may result from excessive consumption should be considered. Future research should elucidate the effects of specific phytochemicals contained in lemons on human health, optimal consumption rates and their role in the prevention of chronic diseases through larger-scale clinical studies. This will provide a better understanding of the supportive effects of lemons and provide stronger evidence for dietary guidelines.

Sources

• Assini, A., Serebruany, V., & Goldberg, M. (2013). Antiplatelet effects of citrus extracts and compounds: A review. Journal of Functional Foods, 5(2), 527-535.
• Ghanim, H., Abuaysheh, S., & Chaudhuri, A. (2011). Orange juice neutralizes the proinflammatory and prooxidant effects of a high-fat, high-carbohydrate meal. The American Journal of Clinical Nutrition, 93(2), 273-278.
• Kumar, S., Al-Ghorbani, M., & Al-Hajar, R. (2020). Citrus Limonoids: A Review of Their Anticancer Activities. Biomolecules, 10(9), 1332.
• Li, S., Wu, D., & Sun, Z. (2014). Antioxidant activities of Citrus flavonoids and limonoids. Food Chemistry, 148, 169-175.
• Maggini, S., Pierre, A., & Calder, P. C. (2017). Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients, 9(10), 1087.
• Slavin, J. L. (2013). Fiber and prebiotics: Mechanisms and health benefits. Nutrients, 5(4), 1417-1435.
• Worcester, E. M., & Coe, F. L. (2010). Citrate and renal stone formation. Seminars in Nephrology, 30(2), 173-181.