25. Nutrition and Osteoporosis

Nutrition in treatment of osteoporosis is currently in the centre of attention of research activities as it contributes to bone quality throughout the whole life, during bone maturation as well as in adulthood. In addition to common therapeutic procedures consisting in pharmacological interventions, nutrition plays one of the key roles in treatment of advanced osteoporosis. This issue is paid increased attention because it is one of the three main factors for achieving peak bone mass at the age of about 25 years. Up to 80 % of peak bone mass is determined by the first factor, i.e. genetic predispositions, which cannot be influenced. The second factor is physical activity during growth stage which has an essential impact on bone mass acquisition and bone quality. Bone loading is the main stimulus for bone regeneration. Regular physical activity during all phases of life is beneficial for bone mass accrual and skeletal health. The third factor is a proper nutritional status during the whole life. This factor becomes even more important in advanced age as osteoporosis is one of the common diseases in the elderly population, affecting predominantly the group of postmenopausal women. Another group where nutrition plays essential role comprises patients who developed osteoporosis in association with another disease which has a negative impact on bone. This is so-called secondary osteoporosis. The underlying causes include drug-induced osteoporosis, mainly after long-term use of corticosteroids, celiac disease and lactose intolerance. Nutrition serves not only as the basic source of energy, but it is decisive also for other processes and bone quality. The basic components of nutrition that influence bone quality include adequate intake of calcium and vitamin D and a balanced intake of proteins, vitamins and trace elements [1]. 25.1 Calcium Calcium (Ca) is the basic building component of bones, and its daily intake should be about 1000–1500 mg depending on age. Ca absorption rate achieves 75 % in childhood and 30–50 % in adulthood and decreases with ageing. It is promoted by the proper level of hydrochloric acid in the stomach, adequate vitamin D level, lactose in food and the proper Ca/P ratio in the diet. The most common Ca sources include dairy products, the absorption rate of which, however, ranges only around 30 %, while in vegetables, such as cauliflower, broccoli, kale, watercress, the absorption rate exceeds 50 % [2]. 25.2 Vitamin D Vitamin D is essential for Ca absorption in the small intestinal loop through active transport mechanism. Adequate absorption of calcium prevents development of secondary hyperparathyroidism and decreases bone resorption. Achievement of optimal vitamin D levels requires sunlight exposure, as vitamin D is activated mainly through skin (80–90 %). In our geographical location zone, two sun exposure units (30 min) weekly are recommended. It has been demonstrated that during autumn, winter and spring most people in our geographical location have low levels of vitamin D. Particularly the housebound elderly have very limited sun exposure, and natural generation of vitamin D is therefore considerably limited. For this reason, supplementation is recommended during winter months (400–800 IU/d), which equals 2 drops of Vigantol per day, or 20 drops once a week. Vitamin D supplementation reduces the risk of fractures from falls and improves the function of lower limbs in the elderly. Research has recently focused also on extra-skeletal effects of vitamin D, such as the proved reduction of incidence of tumours, decreased prevalence and severity of autoimmune diseases (multiple sclerosis, arthritis, juvenile diabetes mellitus) and neuroprotective effect – reduction of the risk of neurodegenerative diseases and blood pressure reduction [2, 3]. Natural foods high in vitamin D include mainly fatty fish and seafood that account for about 20 % of available vitamin D. Vitamin D is currently provided also through food fortification (milk, butter, etc.). 25.3 Proteins Bone matrix is composed predominantly of proteins, such as osteocalcin and collagen. Recent studies have investigated impact of diet on internal environment in direct association with protein intake and a higher share of animal proteins at the expense of plant proteins. Foods can be categorized by the potential renal acid loads (PRAL), as having relatively high acid loads, meats, sugar, hard cheese and fish; neutral acid loads, cereals, grain products, rice and milk; and a negative acid load, fruits and vegetables. It has been proved that proteins increase endogenous production of acids, and, vice versa, plant-based diet contains potassium salts with anions of organic acids (metabolizing after intake into bicarbonate and thus alkalizing internal environment). Increased endogenous production of acids (excessive consumption of meat and proteins) then results in chronic low-grade metabolic acidosis. Buffering of this acidic pH by the alkaline calcium salts in the skeleton leads to bone loss. As a result, long-term diet high in proteins gradually decalcifies bones by the above-mentioned mechanism. For this reason it is recommended to limit reasonably proteins in diet in favour of vegetables. Lack of proteins results in malnutrition and has an impact on both the peak bone mass and maintenance of bone quality in adulthood. In our population, such deficiency relates only to severe conditions [2, 3]. 25.4 Fats Currently, attention is focused on omega-3 and omega-6 fatty acids. A positive influence has been proved of omega-3 fatty acids on bone for their anti-inflammatory effect, on reduction of bone resorption, improvement of intestinal calcium absorption, increased rate of Ca deposition in bone and increase in bone collagen. Omega-3 fatty acids are found primarily in fish fat and certain plant oils (olive, rapeseed, linseed, etc.). 25.5 Fruits and Vegetables The alkalizing effect of fruit and vegetables on homeostasis of internal environment in the organism has been known for a long time. Plant-based diet contains potassium salts with anions of organic acids, metabolizing after intake into bicarbonates and thus alkalizing internal environment. For thousands of years, people had been eating food lower in Na and higher in potassium salts; while at present, our food is rich in acidifying sodium chloride, with potassium salts almost absent in animal products and cereals. In addition, fruits and vegetables contain a wide range of vitamins and minerals, antioxidants and many other bioactive substances having a positive effect on bone [2, 3]. 25.6 Vitamins and Trace Elements In terms of bone metabolism, one of the most important is vitamin K and certain other elements. Vitamin K1 positively influences osteocalcin production; it is involved in osteoblast induction, inhibition of osteoclast production. Its deficit results in decreased bone mass density (BMD) and increased risk of fractures. Vitamin K1 (phylloquinone) is contained primarily in green, leafy vegetables, olive oil, cheese, the liver, soya beans, cereal sprouts, broccoli, cauliflower, green tea, etc. The newly discovered vitamin K2 (menaquinone MK4, MK7), which is contained in soya beans fermented by bacillus subtilis natto, is used as a traditional supplement of the Japanese food. It activates osteocalcin, Gla protein; it reduces Ca excretion, bone resorption, and has a positive effect on BMD. In addition, certain positive effect has been proved of vitamin B6, vitamin B12, vitamin A, magnesium, trace elements of zinc and selenium, copper, manganese and boron. Recent investigations have focused on another trace element, strontium, and its osteoblastic and antiresorptive effect. Strontium can be found in water and soil (0.01–0.45 mmol/l) and certain foodstuffs (0.023–0.046 mmol/l). It has a complex effect on bone apatite crystals and has affinity for dental tissue. In general, strontium is contained in spices, seafood, whole grain bread, root and green, leafy vegetables and legumes [2, 3]. 25.7 Balanced Diet Based on the above given facts, the following basic principles of balanced diet have been recommended by WHO (Fig. 25.1). This diet should comprise about 15 % of proteins with prevalence of fish and white meat. The ratio of fat should be 30–40 %, with preference given to unsaturated fatty acids. They include plant oils, such as olive, rapeseed, linseed oil and nuts. Of animal fats, fatty fish is recommended for a high content of omega-3 fatty acids. Carbohydrates should prevail in a balanced diet, up to 45–55 %, mainly in the form of vegetables, fruits, legumes and fibre-rich foods with low glycemic index (rice, whole grain pasta, potatoes) [4, 5]. Fig. 25.1 Composition of a balanced diet (According to WHO) × General and nutrition factors preventing development of osteoporosis, including major risk factors: Age is a major risk factor – osteoporosis is common in advanced age when the supply of all nutrients often becomes limited and one-sided – insufficiently varied diet. Underweight in youth (BMI 18.5) – mental anorexia and long-term psychiatric disorders. Alcohol – excessive consumption has a negative impact on bone. Weight reduction diets causing underweight, primarily in young individuals, have a negative impact on BMD (bone mass). Strict diets result in imbalanced and one-sided supply of nutrients. Low body weight may result in inadequate loading of bone, which is the main stimulus for its regeneration. Acidifying effect on internal environment is associated, for instance, with consumption of sugar-sweetened soft drinks (coca-cola, etc.), excessive intake of proteins, salt and caffeine – more than five cups of coffee daily (with excessive amount of sugar). In terms of nutrition and its effect on bone, it is important to know that: A lifelong balanced diet is a prerequisite for healthy bones, similarly as a healthy lifestyle with a focus on factors improving bone quality (mainly physical activity) and elimination of risk factors. An organism needs sufficient supply of vitamin D: optimal annual level should be achieved through sun exposure, food fortification and regular consumption of fatty fishes or supplements. Introduction of vitamin K2 in the treatment of osteoporosis in future, a balanced sodium-potassium ratio in the diet and adequate supply of trace elements, such as magnesium, zinc, selenium, copper, boron, and strontium, in a varied diet is a way to prevent osteoporosis.

Medicine Matters Rheumatology

25. Nutrition and Osteoporosis

Abstract