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brief summary annotation: -list strength and weaknesses-main argument-author background-relevance to topic (my topic is how micronutrient and macronutrient needs have adverse effects on bone atrophy (stress fractures) amongst athletes )Nutrient effects on stress reaction to bonePain complaints related to periostitis and stress fractures are common in active individuals. This spectrum of “stress reaction” to bone is usually associated with untrained athletes who are making a lifestyle choice and beginning activity, or conditioned athletes who increase the intensity, frequency, or duration of training.The role of calcium and vitamin D in bone health is undisputed. Since 1997, the Canadian and American governments have recommended a daily allowance for vitamin D for adults of 600 IU per day. Many experts believe this value is inadequate and continue to advocate for a higher recommended daily allowance for vitamin D.  In 2007 the Canadian Cancer Society recommended a daily intake of 1000 IU of vitamin D, advocating for the beneficial effects of vitamin D in the prevention of colorectal, breast, and prostate cancer.  Vitamin D is synthesized in the skin; UVB solar exposure converts 7-dehydrocholesterol to vitamin D. In Canada there is a seasonal variation to vitamin D synthesis, with levels at their lowest in the winter months.  About 20 000 IU of vitamin D are produced from a single 15-minute, midday, whole-body exposure to sunlight. However, this is negatively affected by clothing and sunscreen. In winter months, at latitudes beyond 42°N the solar angle is too oblique for vitamin D synthesis, contributing to increased deficiency between October and April. Food-source supplementation has become the main source of vitamin D where solar exposure is limited. Food products provide about 200 IU of vitamin D per day. Health Canada recommends that, in addition to following Canada’s Food Guide, those older than 50 years of age should take a daily vitamin D supplement of 400 IU daily.Vitamin D is required at all phases of skeletal development and is essential for the mediated transport of calcium to produce mineralized bone matrix. Bone resorption markers are detected with vitamin D levels less than 60 nmol/L, and parathyroid hormone (PTH) increases with vitamin D levels less than 78 nmol/L. Inadequate vitamin D results in secondary hyperparathyroidism, increased bone turnover, accelerated bone loss, and increased fracture risk.Previous research has variably demonstrated both positive and negative relationships between calcium and vitamin D levels and stress fractures. Previous research identified that athletes with stress fractures had lower calcium intake. Calcium supplementation has a positive linear relationship to spinal trabecular bone density in amenorrheic elite athletes. But calcium intake did not correlate with stress fractures and bone mineral density in female army recruits, and calcium in the diet did not alter stress fractures in elite cross-country athletes. Vitamin D levels have been shown to be lower in Israeli military personnel with stress fractures,14 but calcium and vitamin D levels have not been related to stress fractures in adolescent girls. In 179 Finnish military recruits, stress fractures were associated with high PTH levels but not low vitamin D levels. Because Finnish men have poor vitamin D status, vitamin D supplementation to lower PTH and reduce the incidence of stress fractures was recommended.16 In another study, serum vitamin D was significantly lower among 756 Finnish military recruits in those with stress fractures (odds ratio = 3.6, 95% CI 1.2 to 11.1). More recent studies have identified a 20% decrease in stress fractures in American military recruits using calcium and vitamin D supplementation. The balance of current research provides evidence to suggest that maintaining adequate vitamin D status might reduce stress fracture risk in athletic populations.Vitamin D deficiency is common in Canada and at latitudes above  Sunscreen and clothing limit vitamin D synthesis in the summer months, and exposure to solar radiation is insufficient in winter months to affect vitamin D production. Normal calcium metabolism is dependent upon adequate intake of calcium and vitamin D, but an excess of one can partially compensate for a deficiency in the other. The effect of calcium and vitamin D on bone metabolism has been confirmed in the osteoporotic population but might be underappreciated in the healthy, active population.Periostitis and stress fractures are 2 entities along the spectrum of stress reaction to bone. Bone is a specialized form of connective tissue. In the adult, bone comprises 35% organic material that is mainly type 1 collagen; 60% mineral, mainly calcium hydroxyapatite; and 5% water. Like other tissues, bone responds to stress. Weight-bearing activity results in stress-generated potentials that affect the orientation of collagen fibres and the mineral deposition in bone. Bone remodels in response to mechanical stress and is affected by the number of loading cycles, cycle frequency, amount of strain, strain rate, and strain duration per cycle. When bone is loaded, bending of the collagen molecules under compression results in electronegative forces, and the area under tension creates electropositive forces. Osteoclasts dissolve the crystalline and collagen structure of bone and are stimulated by electropositive forces created from tensile forces. Activation of osteoclasts causes microfracture and debonding at the cement lines of the haversian canal in the basic unit of bone. Each loading cycle results in a small amount of strain energy lost through microscopic cracks along the cement lines of the haversian system. Progressive accumulation of microdamage results in bone failure through crack propagation when remodelling and new bone formation cannot keep up with the progressive bony remodeling.1 With accumulation of stress response to bone, a spectrum exists from normal remodeling of bone to excessive remodeling, which results in weakening of the bony trabeculae and microfracture. Proliferation of periosteum occurs along areas of microfracture. If the stress to the bone is not altered, the progressive microfracture results in macrofracture. Increased levels of unaccustomed activity together with insufficient time for recovery result in the progressive accumulation of microfracture and stress fracturing of bone.Muscles exert a protective effect on bone. Muscle contraction causes a reduction in cortical bone surface bending strain and diminishes the electropositive forces on the bone. With muscle fatigue, the shock-absorbing effect is diminished and more force is transmitted directly to the bone, increasing the microdamage accumulation. Intrinsic factors such as sex, race, age, bone geometry, foot structure, and leg length affect the stress reaction to bone. So do external hip rotation, lower limb biomechanics, hormonal factors, and bone mineral density. Extrinsic factors such as the training regimen, training surfaces, footwear, aerobic fitness and muscle strength, medications, and smoking also factor into the stress reaction to bone. There are also general medical issues, such as the female athlete triad, and the nutritional influences of caffeine, calcium, and vitamin D that play a role in the stress response to bone.For a number of years, I have been successfully treating patients who have periostitis or stress fractures with 1500 mg calcium and 1000 to 2000 IU vitamin D, without regularly altering levels of training or weight-bearing exercise. Between July 2007 and June 2010, a random sample of 33 patients (8 men and 25 women) presenting with a clinical diagnosis of stress fracture were evaluated for calcium and vitamin D adequacy by measuring serum calcium and vitamin D levels. No one in this sample population demonstrated deficiencies in serum calcium levels, but 4 men (50%) and 11 women (33%) were clinically deficient in vitamin D, with serum levels less than 80 nmol/L. The importance of this is uncertain, as vitamin D deficiency has a high prevalence in the general population. A recent Statistics Canada study identified that 2 out of every 3 people in Canada have levels of vitamin D below the amounts research has associated with reduced health risks. One in 10 Canadians has a level below that needed for bone health, and about 4% of Canadians have levels of vitamin D sufficiently low to be at risk of rickets.In many areas of Canada, the results of vitamin D investigation are not available in a timely manner. Screening for serum vitamin D levels is not advised for the generally healthy population, and should be restricted to those who are at higher risk of vitamin D deficiency such as elderly individuals, breastfed infants, individuals with dark skin, or those with malabsorption syndromes or limited sun exposure. Athletes with a history of stress fracture, frequent illness, bone or joint injury, skeletal pain, or overtraining syndrome should be screened.19 Athletes who have restricted eating patterns (eg, vegetarian, vegan) or athletes who spend most of their time training indoors should also be screened for vitamin D deficiency. Monitoring the response of patients who are deficient in vitamin D is appropriate 3 to 4 months after initiating vitamin D therapy, but it is not necessary to monitor routine supplementation in otherwise healthy individuals.I recommend that all of my patients with periostitis and stress fractures take 1500 mg of calcium and 1000 IU of vitamin D daily in the summer months (2000 IU of vitamin D in the winter months). Excessive calcium can result in constipation, kidney stones, renal insufficiency, and vascular calcification, and can impair iron and zinc absorption. However, these effects are rare from dietary or supplemental calcium intake and are more commonly associated with primary hyperparathyroidism and malignancy. Excessive vitamin D levels result in nonspecific adverse effects of anorexia, weight loss, and polyuria. They can also lead to increased calcium levels and cardiac arrhythmias. However, symptoms of toxicity are unlikely at supplementation levels less than 10 000 IU daily.ConclusionSupplementation with calcium and vitamin D aids in optimizing bone health and might reduce the incidence of stress reaction to bones in active individuals. However, there are many other factors that contribute to athletic-induced stress reaction to bone, and further large population-based studies are needed to better understand the roles of calcium and vitamin D. Science Biology