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Minerals
Chapter 9
Nutrition for Sport and Exercise
Dunford & Doyle
Learning Objectives
 Classify minerals and describe their
general roles
 Explain how mineral inadequacies and
excesses can occur and why each might be
detrimental to performance and health
 Describe the factors that increase,
maintain, and decrease bone mineral
density, including a discussion of the
minerals associated with bone formation
and their effects on performance and health
Learning Objectives
 Describe the role of iron in red blood cell
formation and the impact of low iron intake
on performance and health
 Describe the roles of minerals in the
immune system
 Compare and contrast minerals based on
their source—naturally occurring in food,
added to foods during processing, and
found in supplements—including safety
and effectiveness
Introduction to Minerals
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Minerals differ from vitamins in many ways
Inorganic (non-carbon containing) compounds
Not well absorbed
Not easily excreted
Medical tests can help measure amount in the
body
21 Essential Minerals
Classification of Minerals
 2 categories based on amount found in
body:
• Macrominerals – found in large amounts
• Microminerals – found in small amounts
• Also known as “trace” minerals
Classification of Minerals
 Functionality
• Proper bone formation
Ex/ Ca, Phos, Mg, Fl
• Electrolytes
Ex/ Na, K, Cl
• Red blood cells
Ex/ Iron
• Enzyme-related functions
Ex/ Zn, Se, Cu
Recommended Daily Mineral Intake
 Dietary Reference Intakes (DRI)
• How much is enough?
 Tolerable Upper Intake Level (UL)
• How much is too much?
 DRI’s established on 15 minerals
 UL established for 16 minerals
 Each mineral needed for proper
physiological functioning and good health
 DRI is the standard for athletes
DRI and UL for Adult Males and Adult,
Nonpregnant Females
The Influence of Exercise on Mineral
Requirements
 Mineral loss in sweat and urine may be
greater in athletes
• Ex/ Sodium, chloride, potassium
 Some minerals may be conserved by body
and not as much will be lost in sweat
 Small to moderate losses can be offset by
dietary intake
 Larger losses may need supplementation
 Consumption of excess minerals can be
detrimental to athlete
• Ex/ Iron, zinc
Average Mineral Intakes by Sedentary
Adults and Athletes
 Men typically consume more minerals than
women
 Many men and women do not consume an
adequate amount
 In athletes, adequate mineral intake is
associated with adequate caloric intake
 Likely if deficient in iron and zinc, that also
deficient in other trace minerals (Martinez et al, 2011)
 If restricting caloric intake, mineral-fortified
foods are helpful
Average Mineral Intake in U.S.
Mineral Deficiency and Toxicity
 Homeostasis is generally maintained by
the body by adjusting absorption and
excretion
• If storage is high, absorption decreases
• If storage is low, absorption increases
 Hormonal and other mechanisms are also
influential
• Ex/ Calcium – absorption, excretion,
resorption all are regulated by hormones
Factors Influencing Mineral Absorption
Competition
 Minerals can compete with each other for
absorption
• Divalent cations (two positively charged ions)
use same binding agents and cellular receptor
sites
Calcium
Iron
Zinc
Copper
Magnesium
Phytates, Oxalates, and Insoluble Fiber
 Phytates and oxalates inhibit absorption of
iron, zinc, calcium, manganese by binding
with the mineral and blocking absorption
• Spinach, Swiss chard, seeds, nuts, legumes
 Insoluble fiber decreases absorption of
calcium, magnesium, manganese, zinc by
decreasing transit time
• Contents of GI move more quickly through GI
tract resulting in less contact time with
mucosal cells
Clinical and Subclinical Mineral
Deficiencies
 General characteristics
• Deficiencies develop over time
• No signs or symptoms initially
• Signs or symptoms are subtle and nonspecific when they first occur
• Specific symptoms associated with severe
deficiencies
Prevalence of Subclinical Mineral Deficiencies
 Ex/ Iron deficiency without anemia
• Subclinical iron deficiency
• In U.S., 14% of children (aged 1-2 yrs), 4% of
children (aged 3-5 yrs), 9% of females (aged
12-49 yrs) (CDC 1012)
• Estimates in female adolescent and adult
athletes range from 25-36% (Auersperger et al, 2013)
• Prevalence may be higher in female
vegetarians
• Effect on performance not known, but it is
prudent to avoid this condition
Prevalence of Subclinical Mineral Deficiencies
 Ex/ Osteopenia
• Subclinical calcium deficiency
• Low bone mineral density
• In U.S., 49% of women and 30% men >50 yrs
old (Looker et al, 2010)
• Estiamtes of athletes range from 11-22%
(Hoch et al, 2009)
• May be as high as 50% of amenorrheic
female distance runners and ballet dancers
 Subclinical deficiencies of other minerals
not well documented
Prevalence of Clinical Mineral Deficiencies
 Ex/ Iron-deficiency anemia
• Clinical iron deficiency
• In U.S., 3% of females 12-49 years old (CDC, 2012)
• Prevalence in female athletes estimated to be 3%
or more
• Prevalence in male athletes very low, but not zero
• Results in fatigue and impaired performance d/t
reduced aerobic capacity and endurance
• Iron deficiency anemia in distance runners higher
than general population (Malczewska et al., 2000)
Prevalence of Clinical Mineral Deficiencies
 Ex/ Osteoporosis
• Clinical calcium deficiency
• In U.S., 8 million women and 2 million men >50
years old (Nat’l Osteoporosis Foundation, 2010)
• Loss of calcium from bone exacerbated when
estrogen production declines d/t menopause
• Amenorrhea (cessation of menstruation) can occur
d/t prolonged low kcal intake
• 10-13% of female distance runners <30 years of
age with amenorrhea (Khan et al., 2002)
• 6-7% of amenorrheic female elite distance runners
under 40 yrs have osteoporosis (Pollock et al, 2010)
Subclinical and Clinical Deficiency
 Clinical mineral deficiencies can negatively
affect performance and undermine the
athlete’s health
 Subclinical mineral deficiencies can impair
an athlete’s ability to train or perform and
put athlete’s health at risk
 “The best defense is a good offense”
 Important to consume nutrient-dense foods
in sufficient quantities to meet caloric needs
Toxicity
 Mineral toxicities are rare, but do occur
 Mineral supplementation has grown d/t:
• Link between minerals and chronic diseases
• Increased advertising for supplements
 Supplement carefully to avoid toxicity
 More people supplementing with single
minerals in higher amounts than would
occur naturally in foods
 More foods now fortified with minerals
Multimineral Supplement
Bone-forming Minerals
 At least 8 minerals involved in bone formation
 80-90% of bone mineral content is calcium
and phosphorus incorporated into
hydroxyapatite crystals
 Small amount of fluoride
 Several minerals have indirect roles
• Magnesium – helps regulate bone metabolism
• Iron, zinc, copper – part of enzymes needed for
collagen synthesis
Bone Growth and Turnover
 3 major bone growth processes:
1. Growth
•
Longitudinally (in length) and radially (in
thickness) – in children, adolescents
2. Modeling
•
Bones are reshaped in response to mechanical
force (weight-bearing activities) – mostly in
children, adolescents
3. Remodeling
•
Old bone that has been microdamaged is
replaced by new bone – mostly in adults
Bone Remodeling
 Skeletal mass consists of:
1. Cortical bone
• ~ 80% of skeleton
• Shafts of the long bones and on the surface
• Compact in concentric circles
2. Trabecular bone
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•
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~ 20% of skeleton
Ends of the long bones and under the surface
Honeycomb-like structure
Greater surface volume, metabolic activity, and
turnover (Sherwood, 2013)
Trabecular and Cortical Bone
Bone Remodeling
 Rate
• 1-2% of entire skeletal mass in adults is being
remodeled at any given time, but 20% of the
trabecular bone is being remodeled
• 10,000-20,000 new remodeling sites each day
• 1 million sites active at any given time
• Adult’s skeleton will have been completely
remodeled over 10 years’ time
Bone Remodeling
 Length of time for remodeling at a certain
site (Heaney, 2001)
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•
•
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In children → weeks
In young adults → ~3 months
In adults → ~6-18 months
Most of time is spent in bone formation, not
breakdown
Bone Remodeling
 “Bone turnover” is constant throughout life
• Process of existing bone being resorbed and new
bone being formed
 Osteoclasts are cells that resorb bone
• Stimulated by physical activity and microfractures
• Stimulated by hormones – PTH and calcitriol
 Osteoblasts are cells that form bone
 Osteoclast/osteoblast balance
• In children and adolescents, deposition is favored
• In young adults, balance generally exists
• In middle aged to older adults, resorption is favored
Peak Mineral Density (PMD)
 PMD is the highest bone mineral density
achieved during one’s lifetime
 ~ 40 to 60% of PMD is genetically determined
 Increased mineral content until ~ age 35
• 95% adult skeleton formed by age 20
• 5% formed age 20-35 years (Rizzoli et al, 2010)
• PMD of trabecular bone achieved b/w 20-30
years of age
• PMD of cortical bone achieved b/w 30-35
years of age
Major Factors the Influence Peak Bone Mass
Figure 9-3 p339
PMD
 Nutritional factors affecting PMD
• Low calcium intake during childhood and
adolescence can reduce PMD by 5-10%
• Achieving PMD is critical to long-term health –
average life expectancy 78.7 yrs (Hoyert and Xu, 2012)
• Vitamin D
Severe deficiency can cause rickets, increased
fractures, impaired bone growth/deformities
• Adequate protein intake in children associated
with bone growth and PMD
Amino acids needed to build matrix around bone
PMD
 Mechanical factors affecting PMD
• Weight-bearing exercise stimulates bone to
increase bone mineral content over time
• Physically active people generally have
greater bone mineral density than those who
are sedentary
• Exercise-related factors that influence PMD:
Type, intensity, frequency of exercise
Age at which exercise was begun
Number of years exercise continues
• High impact activities should be encouraged
Having fun while building bone mass!
Figure 9-4 p340
Bone Loss is Associated with Aging
 Natural consequence of aging
 Slow mineral loss after ~ age 35
 Accelerated mineral loss in females when estrogen
production declines (menopause)
 Bone resorption increases with age and estrogen
deficiency
• Incomplete bone formation occurs when bone resorption
outpaces bone formation
• Formation may not equal resorption during remodeling
 If dietary calcium is low, body must use calcium
reserves in bones to meet metabolic demands
Bone Loss is Associated with Aging
 In women →
0.5 – 1.0% bone loss yearly until age 50
 With estrogen deficiency (menopause) →
1 – 2% bone loss yearly
 In older men →
~ 1% bone loss yearly
Calcium Homeostasis
 Definition: Regulation of calcium in the
blood and extracellular fluid (ECF)
 Primarily controlled by PTH, also calcitriol
 Normal blood calcium 8.5-10.5 mg/dl
 Calcium level is tightly regulated by
hormones (PTH and calcitriol) since it is
critical for proper nerve and muscle function
 Half of calcium in blood is bound to proteins
and half is “free”, unbound – known as
ionized calcium (IC)
Calcium Homeostasis
 Calcium can be quickly moved into the
ECF when concentrations are low – known
as “fast exchange”
• PTH activates calcium pumps in membranes
surrounding bone fluid
• Calcium is mobilized from bone fluid (not
mineralized bone)
• PTH also stimulates calcium resorption in
kidney and activates calcitriol, which
stimulates increased GI absorption of calcium
Calcium Regulation
Calcium Balance
 Describes the body’s total absorption,
distribution, and excretion of calcium
 Different from calcium homeostasis, but
related
 Many people do not consume enough calcium
daily, which affects balance
 Absorption and excretion can be increased or
decreased as needed to maintain balance
 Bone turnover is balanced under normal
conditions
Calcium Absorption
 In adults ~30% of calcium entering the GI
tract is absorbed
• So, a 1,000 mg daily intake of calcium from
food will result in about 300 mg being absorbed
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Amount absorbed regulated by vitamin D
Absorption in adults ~10-50%
Absorption in children as high as 75%
Absorption from supplements varies
depending on composition, ranges 25-40%
Long-Term Low Calcium Intake
 Bone turnover is not balanced
 “Slow exchange” of calcium
• Used to make available the calcium needed due to
inadequate dietary intake
• PTH stimulates dissolution of bone
• Increases osteoclastic activity and decreases
osteoblastic activity
• Calcium (and phosphate) released from bone
Calcium used to maintain blood calcium in normal range
Phosphate excreted in urine
• Over time, integrity of bone is decreased
Bone Loss is Associated w/ Lack of Estrogen
 Decrease in estrogen is associated with
an increase in osteoclast proliferation and
activity
 Estrogen deficiency may be associated
with increased erosion depth in trabecular
bone
 Estrogen deficiency d/t menopause (>50
years) or amenorrhea / oligomenorrhea
(absent or irregular menstruation)
• Distance runners, ballerinas, gymnasts at risk
Bone Loss is Associated w/ Lack of Estrogen
 When both energy and estrogen
deficiencies are present in exercising
women, bone formation is suppressed and
bone resorption is increased (De Souza et al, 2008)
• This predisposes women to failure to achieve
PMD, loss of calcium from bone, alterations in
bone structure, greater incidence of stress
fractures, osteopenia, and osteoporosis
(Ackerman et al, 2011)
• Estrogen deficiency not only associated w/ age!
Preventing or Reducing Bone Loss
Associated with Aging
 Loss of calcium can be slowed by 1% per
yr b/w attainment of PMD and menopause
via adequate intake of calcium
• Bone calcium loss reduced/prevented in many
middle-age men and women if calcium intake
is adequate (Bonura, 2009)
 Calcium when supplemented w/ vitamin D
may reduce risk for fracture in elderly
(DIPART, 2010)
Preventing or Reducing Bone Loss
Associated with Aging
• In women after age 70, calcium
supplementation is beneficial (Morgan, 2001)
• Calcium intake is usually inadequate
• Reduced vitamin D absorption/conversion
 Exercise-related
• High-intensity weight-bearing activities
• Resistance training
• Other types of exercise are beneficial, but do
not slow bone loss
It is Important to Meet the Recommended
Dietary Intakes for Calcium and Vitamin D
Recommended Dietary Intakes of Calcium
 Calcium – DRI updated in 2010
• Greatest amount needed for ages 9 to 18 yrs
DRI is 1,300 mg/day
• Substantial need throughout adulthood
DRI is 1,000 to 1,200 mg/day
Average adult female intake is ~ 650 mg/day
from food (only ~30% absorbed)
Average adult male intake is ~ 925 mg/day
• Tolerable upper intake
• 2,500 mg/day for age 50 and less
• 2,000 mg/day for age 51 and up
• At risk for kidney stones if exceed TUL (IOM, 2010)
Dietary Strategies for Adequate
Consumption of Bone-Related Minerals
 Calcium sources
• Milk and milk products
8 oz glass of milk = 300 mg Calcium
• Yogurt, cheese, ice cream
• Reduced lactose or lactase-treated milk
products
• Some green leafy vegetables
Cabbage, broccoli, greens
• Calcium-fortified foods
OJ, cereal, sports bars, soy milk
• Calcium supplements
Milk and milk products are excellent sources of
calcium.
Those with lactose intolerance may use some of the
products shown, which allows them to include
calcium-dense dairy foods in their diets.
Dark green vegetables are good nondairy sources of
calcium. 1 cup broccoli = ~100 mg calcium.
Soy milk and rice drinks are often
fortified with calcium.
Dietary Strategies for Adequate Consumption
of Other Bone-Related Minerals
 Phosphorus, fluoride, and magnesium
involved in bone health
• Phosphorus is abundant in food; deficiency
unlikely
• Fluoride is added to vitamins or water
Contact local water agency for fluoride content of
tap water
• Magnesium is in green leafy vegetables, nuts,
beans, seeds, whole grains, hard water
Roles of Minerals in Blood Formation
 3 types of cells in blood:
• Erythrocytes – RBCs
• Leukocytes – WBCs
• Platelets – assists with clotting
 Functions of Erythrocytes
• Primary: Transport oxygen
• Secondary: Transport CO2, nitric oxide
Roles of Minerals in Blood Formation
 Hemoglobin
• “heme” = iron; “globin” = protein
• Iron-containing protein found in the RBCs that can
bind oxygen
• Iron (Fe) is at the center of heme portion
4 bonds with nitrogen
1 bond with amino acid
1 bond with oxygen
Each Hgb molecule contains 4 heme molecules
• Normal Hgb levels 15 g/dl (males), 14 g/dl (females)
• 30 trillion RBCs – each contains > 250 million molecules
of hemoglobin
Simplified Hemoglobin and Heme
Molecules
Roles of Minerals in Blood Formation
 Sufficient oxygen-carrying capacity is
critical for athletes, especially endurance
athletes
 Hematocrit
• Amount of RBCs in total volume of plasma (%)
• 42% for women and 45% for men is normal
 Anemia
• Reduced oxygen-carrying capacity
• Hematocrit < 30%
• Nutritional or non-nutritional
Nutritional Anemia
 Nutritional anemias are a result of nutrient
deficiency d/t low intake or poor absorption
 Iron deficiency is the most prevalent
 25% of body’s iron is stored in liver,
spleen, and bone marrow
 Most adults have sufficient iron stores
• Some males with maximum iron storage could
sustain normal Hgb levels for up to 2 years
while consuming an iron-poor diet (Shah, 2004)
Anemia
 Some adults may experience higher-thannormal blood loss resulting in iron deficiency
• GI bleed
• Surgery
• Menstruation
 Iron deficiency anemia results in decreased
number of RBCs, smaller cells, and lower
concentration of Hgb per cell
 Fatigue is most common symptom of iron
deficiency
Figure 9-12 p351
Anemia
 Ferritin
• Storage form of iron
• Amount of ferritin circulating in blood indicates
amount stored
• As amount of storage iron declines, the
amount of ferritin in the blood declines
• Repeated tests over time are valuable
• Ex/ An athlete has ferritin level checked every 6
mos: 120, 110, 85, 63
• Ferritin < 100 ng/ml may be referred to as
“functional iron deficiency”
Iron Deficiency, Iron-Deficiency Anemia,
and Performance
 Iron-deficiency anemia impairs performance
• VO2max (aerobic capacity) can decline 10-50%
due to impaired oxygen transport (Haas & Brownlie, 2001)
• Endurance capacity declines
 Aerobic capacity does not appear to decline
in iron deficiency without anemia
(subclinical deficiency) – normal Hgb, HCT
and oxygen transport is normal
 Recommendation is for athletes to maintain
a normal iron status
Prevalence of Iron Deficiency and
Iron-Deficiency Anemia in Athletes
 Unlikely in most males
• Occasionally seen in adolescent males or male
endurance athletes
 Female adolescent and adult athletes
• Research indicates range from 25-36% (Auersperger
et al, 2013)
 Some medications induce bleeding and
loss of iron (aspirin, ibuprofen)
 Greatest risk is for menstruating females
Prevalence of Iron Deficiency and
Iron-Deficiency Anemia in Athletes
 Athletes with low caloric intake at greater risk
 Be careful of false (runner’s) anemia – Hgb
is low d/t plasma volume expansion associated
w/ endurance training
• Actual Hgb amount is normal but is “diluted”
 High-volume endurance training results in
inflammation, which stimulates hepcidin
• Hepcidin = hormone that influences how much iron
absorbed and transported out of cells
• Hepcidin & iron decreased in female distance
runners engaged in high-volume training
(Auersperger et al, 2013)
Dietary Strategies for Adequate
Consumption of Blood-Related Minerals
 DRI for females aged 19-50 is 18 mg vs.
DRI for males aged 19-50 is 8 mg
• Females lose iron through menstruation and
must replace it via diet
 Adequate energy intake
 6-7 mg iron typically consumed for every
1,000 kcals (in U.S.)
 Variety of iron-dense foods
• Iron is found in many foods, but often in small
amounts.
• Adequate dietary iron intake is associated with
adequate energy intake.
Table 9-13 p353
Dietary Strategies for Adequate
Consumption of Blood-Related Minerals
 Heme sources are better absorbed (15-35%)
than nonheme sources (2-20%)
• Heme = animal
• Nonheme = plant
 Vitamin C increases nonheme iron absorption
 “MFP factor” – consuming animal food with
plant food enhances nonheme absorption
Dietary Strategies for Adequate
Consumption of Blood-Related Minerals
 Copper
• Copper-containing enzyme is needed for RBC
formation
Necessary for conversion of iron from its storage
form (ferrous) to its transport form (ferric)
• Seafood, nuts and seeds are best sources,
also dried beans, whole grains and some
green leafy vegetables
• DRI is 900 mcg
• Excessive zinc can interfere with copper
absorption
Minerals and Immune System Function
 Intense training and prolonged exercise are
immunosuppressive
• Marathon runners have greatly increased risk
for URI (Nieman, 2008)
 Moderate exercise improves immune system
function
 Adequate protein and total energy intake
associated with proper immune system
function
 Also, inadequate intake of zinc, magnesium,
and selenium impairs immune response
Minerals and Immune System Function
 Zinc
• Cofactor in > 200 enzyme systems
• Involved in various immune functions
• DRI
8 mg/day for females
11 mg/day for males
• Zinc deficiency results in damaged skin & GI cells
• Excessive intake of zinc decreases lymphocyte
response and inhibits copper and iron absorption
• Most endurance athletes (90%) do not meet DRI
• Sources: red meat, milk
Minerals and Immune System Function
 Selenium
• Involved in cellular and immune system
function
• Depressed immunity associated with
selenium deficiency
• Athletes not typically deficient in selenium
• Sources: meat, fish, poultry, whole grains,
and nuts
 Iron
• Plays important role in immune system
functions
• Greater risk for infection if iron deficient
• Excessive iron impairs immune function
Adequate Intake of All Minerals
 Tips for obtaining minerals from food:
1. Consume adequate kcals daily
2. Eat a variety of nutrient dense foods that are
minimally processed
3. Consume adequate amount of calcium and
iron in diet
“Rule of thumb” – if Ca and Fe intake is sufficient
in diet then other minerals likely sufficient as well
4. Avoid high sugar/high fat diets – they often
do not meet daily mineral requirements
A nutritious diet contains adequate kilocalories and a
variety of foods, such as those shown here.
This dietary pattern is likely to provide sufficient
carbohydrates, proteins, fats, vitamins, and minerals.
An Example of a High-Fat, High-Sugar,
Low-Fiber Diet
An Example of a Nutrient-Dense, WholeFoods Diet
Mineral Fortification or Supplementation
 Mineral-fortified foods
• Some foods have many minerals added
Cereals, energy bars
 Multimineral supplements
• Dosages may exceed the DRI or UL
• Degree of absorption is not known
• Minerals often decrease absorption of other
minerals
Supplementing with Individual Minerals
 “Food First, Supplements Second” philosophy
 Calcium and iron are most common
 Should be physician-prescribed, not selfprescribed
 Likely to affect absorption of other minerals
 High bioavailability may not be desirable
• Bioavailability refers to the degree to which a
substance is absorbed, utilized, and retained in the
body
• Goal is adequate bioavailability, not high
bioavailability
Chromium Supplements for Athletes
 Chromium picolinate is highly absorbable form
• More chromium absorbed than would be from food
 Enhances insulin sensitivity, glucose utilization
 Excess chromium can result in increased free
radical production, damage to cells
 DRI for adults 20 – 35 mcg (depends on
gender and age)
 Doses less than 200 mcg seem safe
 Effectiveness for increasing muscle mass and
decreasing body fat unclear
Questions?
 Do minerals provide kcals?
 Do minerals provide energy?
 Does exercise increase mineral
requirements about what is recommended
for healthy adults?
 Does iron deficiency anemia impact
athletic performance?
Summary
 More than 20 minerals are needed for the
proper functioning of the body
 Extreme intakes – too little or too much –
are detrimental to health
 Athletes in training are unlikely to need
more than the DRI
 Adequate mineral intake is associated with
adequate caloric intake and a variety of
nutrient dense foods
Summary
• Adequate calcium intake is critical across
the lifecycle to maintain calcium
homeostasis, calcium balance, and bone
mineral density
• Iron-deficiency anemia impairs endurance
performance
• A “food first, supplements second” policy
can serve athletes well