Consumption of citrus fruits such as oranges, lemons, limes, pamelos, and grapefruits can help in the prevention and treatment of chronic non-communicable (diet-related) diseases
Health care professionals, including nutritionists and dietitians argue that diets rich in fruits and vegetables are strongly associated with numerous health benefits and lower risk of disease.
In recent years increasing attention has been given to the sum of biologically active elements found in citrus fruits, particularly their plant-based non-nutrients called phytochemicals, because of the role they play in preventing a range of chronic disease conditions, including cancer and heart disease.
Furthermore, there is considerable evidence that citrus fruits have been shown to have positive associations with bone and immune system health.
Citrus fruits contain a variety of vitamins, minerals, fiber, and phytochemicals, such as carotenoids, flavonoids, and limonoids, which appear to have biological activities and confer health benefits.
The objective of this short review is to present the health benefits of components of citrus fruits with particular emphasis laid on their role in the prevention and treatment of chronic non-communicable diseases.
The flavours provided by citrus fruits are among the most preferred in the world, and it is increasingly evident that citrus not only tastes good, but is also good for people.
It is well known that citrus fruits contain a wide range of key nutrients including high levels of vitamin C and significant amounts of dietary fibre, carotenoids and folates.
They have a low ratio of sodium to potassium (suitable for combating hypertension) and are low in fat and dietary energy, making them nutrient dense, energy-dilute foods with a low glycaemic index. Citrus fruits are also extremely rich in antioxidants.
VITAMIN C: Citrus fruits are an excellent source of vitamin C. Most people can achieve 100% of the recommended dietary allowance (RDA) for vitamin C by consuming moderate amounts of this family of fruits.
Vitamin C being an essential water-soluble vitamin, plays a key role in the production of collagen, a primary component of much of the connective tissue in the body.
Adequate collagen synthesis is essential for strong ligaments, tendons, dentin, skin, blood vessels and bones, and for wound healing and tissue repair. The weakening of these tissues is a symptom of vitamin C deficiency.
Vitamin C plays an important role in the absorption of inorganic iron (iron found mainly in plants); it has also been shown to be useful in the treatment of anaemia and stress.
Vitamin C is also involved in the immune system by stimulating white blood cell function. Vitamin C can help reduce the risk of pre-eclampsia (high blood pressure) during pregnancy.
Contrary to popular belief, vitamin C does not seem to prevent the onset of the common cold, but in some studies it has been reported to reduce the length and severity of the symptoms.
Contemporary interest in vitamin C focuses on its ability to perform antioxidant functions. As an antioxidant, it can help prevent the cell damage done by free radical molecules (waste products of oxygen transformation) as they damage protein, fatty acids and DNA (human genetic material) in the body.
Free radical damage has been implicated in the progression of several diverse and important disease states including cancer, cardiovascular disease and cataract formation.
Being a good source of antioxidants, if regularly consumed, citrus can be an important part of a diet, which can reduce the risk of such chronic disease.
According to the experts of the United States National Academy of Sciences, Food and Nutrition Board, only 10 mg of vitamin C per day are required to prevent vitamin C deficiency and the devastating disease scurvy.
However, for good health and sufficient body storage of vitamin C, 90 to 100 mg/day is generally recommended, although some recent studies have provided evidence that more than 200 mg/day may be optimal for the prevention of chronic disease.
Too much vitamin C (above 500 mg), generally seen with very high levels of supplementation, may be dangerous, especially for those at risk of iron overload (genetic disorder of excessive accumulation of iron in the liver).
Consuming of the recommended five servings of fruits and vegetables each day can result in an intake of about 200 mg of vitamin C.
Citrus fruits are a particularly good source of vitamin C, with one medium orange or grapefruit providing approximately 70 mg and 56 mg, respectively.
A 225 ml glass of orange juice contains approximately 125 mg of vitamin C, but with amount of other important bioactive compounds.
FOLATE: Folate is a water-soluble vitamin essential for new cell production and growth. It helps in the production and stabilisation of the genetic material DNA and ribonucleic acid (RNA) and mature red blood cells, which ultimately prevent anaemia.
In many countries, the recommended daily intake of folate for prevention of neural tube defects, a severe birth defect, is 400 mcg.
Lack of folate is also implicated in higher homocysteine (substance derived from the metabolism of the amino acid methionine) concentrations, which increase the risk of atherosclerosis and heart disease.
Citrus fruits can be a complementary source of dietary folate and can provide up to 10% to 20% of the RDA for adults and children less than 9 years of age, respectively, with just 100 g. In fact, a 225 ml glass of orange juice provides 75 mcg of folate.
CAROTENOIDS: Citrus fruits contain many carotenoids. Carotenoids are terpenes (tetraterpenoids) and are yellow and orange pigments found in abundance in plants; over 600 carotenoids have been identified, but only about 50 are present in the human diet.
. The most abundant carotenoids in the human diet, lutein, zeaxanthin, lycopene, and the pro-vitamin A carotenoids, α- and β-carotene and β-cryptoxanthin, are found in fruits and vegetables.
Carotenoids are antioxidants that have been demonstrated to have positive effects on the immune system, promote bone formation and health, stimulate gap junction communication between cells, promote eye health and lower the risk for the development of many types of cancers.
Carotenoids in fruit are dissolved in the chromoplast as opposed to being bound to proteins in the chloroplasts of dark-leafy green vegetables, and considerable evidence supports fruit carotenoids having higher bioavailability.
Tangerines in particular can provide a substantial amount of the pro-vitamin A carotenoid, β-cryptoxanthin, a carotenoid that appears to be a highly bioavailable source of vitamin A.
Scientific studies have shown that consumption of 100 g of tangerine daily can meet as much as 72% of the recommended daily intake of vitamin A for children. It is worth mentioning that Vitamin A is required by humans for the normal functioning of the visual system.
Another main function of vitamin A is the maintenance of growth and epithelial cellular integrity and immune function in the body. In vitamin A deficiency, the number of goblet cells are reduced in epithelial tissues, resulting in a reduction in mucous secretions with their antimicrobial components.
Cells lining protective tissue surfaces flatten and accumulate keratin because they fail to regenerate and differentiate. All these changes result in diminished resistance to invasion by potentially harmful organisms.
CARBOHYDRATES AND DIETARY FIBRE: The main energy-yielding nutrient in citrus fruits is carbohydrate; citrus fruits contain the simple carbohydrates (sugars) fructose, glucose and sucrose, as well as citric acid which can also provide a small amount of energy. Citrus fruits also contain non-starch polysaccharides (NSP), commonly known as dietary fibre, which is a complex carbohydrate with important health benefits.
The predominant type of fibre in citrus is pectin, making up 65 to 70 percent of the total fibre. The remaining fibre is in the form of cellulose, hemicellulose and trace amounts of gums.
Citrus also contains lignin, a fibre-like component. In the body, NSP holds water-soluble nutrients in a gel matrix which delays gastric emptying and slows digestion and absorption.
This tends to promote satiety, and may reduce the rate of glucose uptake following consumption of glycaemic (available) carbohydrate, thus helping to prevent a surge in blood glucose levels. Improper regulation of blood glucose results in either hyperglycaemia (high blood glucose) or hypoglycaemia (low blood glucose).
NSP can also interfere with the reabsorption of bile acids which may help in lowering plasma cholesterol levels. A reasonable goal for dietary NSP/fibre intake is 25 to 30 g/day, but in many developed countries the actual average intake is closer to 15 g. With one medium orange containing approximately 3.0 g of NSP, citrus fruit can make a valuable contribution to meeting the daily fibre goal.
These are the thoughts of:
Sa’eed Halilu Bawa
Senior Lecturer (Associate Professor) at University of the West Indies, St. Augustine Campus, Trinidad.
Studied Food and Nutrition Sciences, Dietetics at Kaduna Polytechnic, Nigeria; Warsaw University of Life Sciences, Poland.