Approximately 60% of adult bone mass is gained during the adolescent years, with the most rapid bone accretion occurring during late childhood and the pubertal growth spurts. Peak bone mass (PBM), which is to a great extent genetically determined - although hormonal factors and the age of onset of puberty are important determinants - occurs at the conclusion of growth. The key determinants of bone mineral density (BMD) in later life are the amount of peak bone mass achieved and the subsequent rate of bone loss. Together with exercise and hormonal action, nutritional factors play a crucial role in the timely acquisition and maintenance of body bone.
Composition of bones
Bone is a living tissue which is
constantly undergoing change. It consists of an interwoven meshwork of collagen
fibres (the matrix) which are bound together and hardened by calcium phosphate
and small traces of magnesium and fluoride. Regulation of the bone matrix is
the responsibility of osteoblasts, osteocytes and osteoclasts. Osteoblasts
build up new bone and are particularly active during childhood. Osteocytes are
mature bone cells that become imbedded into the bone matrix as they mature from
osteoblasts. These cells serve as a communication network within the bone.
Osteoclasts are responsible for bone resorption. They work in conjunction with
the osteoblasts through a 'coupling' action. As such, when bone resorption
increases, the rate of bone formation also increases. Two primary types of bone
are cortical and trabecular bone. Cortical bone primarily functions to provide
structure and protection, whereas trabecular bone has an active metabolic
function resulting from its contact with bone marrow, blood vessels, and
connective tissue.
Nutritional factors that are
determinants of normal bone mass
Vitamin D is obtained from sunlight and dietary consumption in the
form of Vitamin D3 (cholecalciferol). Calcitriol is the most biologically
active form of vitamin D and increases calcium and phosphorus absorption from
the intestine, induces osteoclast maturation for bone remodelling, and promotes
calcium deposition in bone and a reduction in parathyroid hormone (PTH).
Recent studies suggest that
hypovitaminosis D is more common in children and adolescents than previously
believed, even in notoriously sunny countries. The consequences of
hypovitaminosis D is impaired calcium absorption, increased calcium resorption
from bone and a contributory factor in a wide variety of chronic diseases as
well as common clinical disorders such as low back pain and generalised
musculoskeletal pain.
Vitamin K appears to be involved in several mechanisms essential for bone metabolism, including its positive influence on calcium absorption, its synergistic work with vitamin D on bone metabolism and its inverse correlation with fracture risk. Supplementing with vitamin K for just one month resulted in increased bone formation markers and decreased bone resorption markers in female elite athletes, of whom four where amenorrhoeic.
Calcium is the provider of resistance and rigidity to bone mass and
teeth. The reduction of mineral bioavailability by phytic acid, found in most
grains, seeds and beans, is widely recognised. Phytates form insoluble complexes
with calcium rendering it unavailable for absorption.
Dairy foods have often been cited as
the most important source of calcium yet most studies of dairy food intake and
bone health provided inconclusive results. The group that appears to have the
greatest beneficial effect from the ingestion of dairy products is women under
30 years. The suggestion that protein intake reduces calcium absorption is
strongly disputed. Overall, protein tends to have a positive effect on bone
health.
Magnesium is an important mineral for bone metabolism but is often
ignored. Magnesium levels are decreased with excessive intakes of phosphoric
acid found in carbonated drinks, coffee intake and excessive menstruation. As a
magnesium deficiency can lead to calcium deficiency, the two minerals should be
supplemented together, although good quality supplements will also include
vitamins A, D3 and K. Even though magnesium is readily available in food,
absorption and retention is a complex issue and deficiencies are common.
The typical Western diet is high
inomega-6 polyunsaturated fatty acid (PUFA).
It is thought that our present intake of omega-6 to omega-3 is 20-30:1 whilst
the optimal suggested ratio of these two essential fatty acids (EFAs) is 1-4:1.
Part of the problem is due to our
high intake of grains. Grains contain an imbalanced ratio of EFAs. Although the
total fat content and the amount of omega-6 fatty acids is not significant in
terms of total calories, the ratio of EFAs determines the production of pro or
anti-inflammatory eicosanoids. For example, omega-6, via the eicosanoids
metabolic products from arachidonic acid, induces the production of
pro-inflammatory prostaglandin E2 (PGE2) and omega-3 stimulates
anti-inflammatory PGE3. PGE2 is known to reduce the bone-forming activity of
osteoblasts and to increase the bone-resorbing activity of osteoclasts. Modern
agriculture is thought to be responsible for a decrease in omega-3 fatty acid
content in many foods including meats, vegetables, eggs and even cultured fish.
In addition, our intake of omega-3 fatty acid found in cold water fish has
decreased. As such, our diet has become highly pro-inflammatory with negative
consequences on bone health.
Other considerations influencing
bone mass
Any significant decrease in caloric
intake can have a profound effect on bone health of male and female
athletes, both from a lack of nutrients and from a possible disruption of
hormonal balance. Some athletes are under pressure to maintain a particular
level of body fat composition and appearance to perform in certain sports such
as gymnastics, track and field and figure skating. Extreme dietary restrictions
can lead to endocrine dysfunction, decreasing oestrogen and elevating
glucocorticoid levels resulting in increased bone resorption.
In conclusion, the key to preventing
stress injuries in athletes is to maximise PBM in the paediatric, adolescent
and young adult age group. The key to maximising PBM is to consume a diet
containing a variety of foods at each meal, something that is often lacking in
young adolescents. Clinically, we have found that fruit intake is often optimal
but vegetable intake, particularly the green leafy kind, is well below
recommended levels. As a result, we have often diagnosed magnesium
deficiencies. Increasing fruit intake is not, and must not, be a substitute for
a lack of vegetable intake. Vegetables, of which there is a huge variety, must
form a large part of every adolescent athlete's daily food intake; as should
the reduction or elimination of carbonated beverages. One thing is certain:
without strong bones, our young athletes will never make it to the top of their
sport. 2010 Corpotential, All Rights Reserved.
Tidak ada komentar:
Posting Komentar