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Calcium--Osteoporosis and Blood Pressure

LOUIS L. RUSOFF

Department of Dairy Science

Louisiana State University

Baton Rouge 70803

ABSTRACT

Calcium is the main essential mineral

for building strong bones and sound teeth. Bone remodeling occurs throughout life; new bone is deposited and existing bone is replaced. Peak bone mass de- velopment is obtained up to 35 yr of age after which bone resorption is increased.

It is therefore imperative that Ca intake

meet the recommended dietary allowances not only during the growing period but throughout life. Milk and dairy products are the major food source of Ca in the US diet, supplying about 61% of our intake while other food groups supply the rest.

It is almost impossible to supply the

recommended dietary allowances of Ca without consuming milk in some form, as most other food groups are low in Ca content. The Ca in dairy products is bioavailable and readily absorbed by the body whereas Ca in other food sources may be less so.

Several government surveys have shown

that a large proportion of the US popula- tion, especially females 11 yr of age and older, have very low Ca intakes that do not meet the recommended dietary allowances for Ca. Recent developments in osteoporosis (porous, brittle, and fragile bones) have indicated that low Ca intake or bioavailability of this mineral is one of the major factors involved in this crippling bone disease. Osteoporosis af- fects 15 to 20 million middle-aged and elderly persons, especially postmenopausal women who are susceptible to bone fractures.

Recent studies on nutrient intake and

high blood pressure have reported an inverse relationship between dietary Ca intake and blood pressure levels. Although

Received August 30, 1985.

Accepted March 10, 1986. these reports do not prove causality, they indicate that low consumption of dairy products may serve as a marker for hypertension.

Deficiency of Ca among Americans is

far more serious than the concern over the cholesterol content of dairy products.

Milk and its products (main sources of

Ca) are vital in daily diet to maintain a

strong skeleton and good health into old age.

INTRODUCTION

Dairy products consumed in the US make an

important nutritional contribution to our national diet and to our health. Thousands of scientific studies have proven that milk and its products contain most of the essential nutrients required for good health and supply more of these nutrients (especially proteins, minerals, and vitamins) than any other food (16, 17).

Of the recommended dietary allowances

(RDA) for adults, 30 to 50 yr of age, established by the Food and Nutrition Board, National

Academy of Sciences - National Research

Council (NAS-NRC) (7),

.946L (1 qt)vitamin

D fortified milk supplies a high percentage of

major nutrients (6) (Figure 1) for females (F) and males (M): vitamin D (200% M and F), Ca (145% M and F), P (114% M and F), riboflavin (135% F, 100% M), protein (90% F, 64% M), and a lower percentage of vitamin A (35% F,

28% M), calories (32% F, 24% M), and thiamin

(28% F, 20% M).

For the past several years, health conscious

Americans have reduced their consumption of

milk and its products drastically, mainly because of the fat and cholesterol scare, even though there is no scientific evidence to date that atherosclerosis (clogging of the arteries) or coronary heart disease (CHD) will be prevented or delayed by consuming low cholesterol foods or that milk and its products cause athero- sclerosis or CHD (18). The evidence regarding

1987 J Dairy Sci 70:407-413 407

408 RUSOFF

VII D Ca P Riboflavin protein ',/it. A C=lori~ Th,nm,~

Figure 1. Major nutrients contributed by .946 L

(1 qt) of vitamin D fortified milk compared with the recommended dietary allowances (RDA) for an adult. 30 to 50 yr of age.

low cholesterol diets for healthy Americans is still intensely controversial. By reducing their consumption of dairy products, health conscious

Americans have been shortchanging their

nutritional needs, especially of Ca, one of the major factors involved in osteoporosis and high blood pressure. The positive nutritional and health contributing values of dairy products appear to outweigh concerns regarding cho- lesterol.

Calcium

The mineral in greatest quantity in the

human body is Ca, comprising about 2% of the total weight of an adult (approximately 1400 g for an average man). The importance of Ca and

P in the diet for building strong bones and

sound teeth is well-known. Although 99% of the body's Ca is present in bones and teeth, the remaining 1% is very essential in all living cells as it is involved in many biological processes. It activates certain enzyme systems; controls neuromuscular excitability; is involved in maintenance of normal heart beat, blood clotting, hormone secretion, muscular contrac- tion, and cell wall permeability (16).

Recommended Dietary Allowance for Calcium

The allowance ranges from 360 mg for

infants to 1600 mg for pregnant or lactating women. For children 1 to 10 yr of age and adults 19 to 51 + yr of age, the RDA is 800 mg; for boys and girls 11 to 18 yr of age, PDA is

1200 mg (7). Consumption of .946 L (1 qt) of

milk or its Ca equivalent in dairy products will supply approximately 1200 mg Ca. Dietary Sources of Calcium

Milk and dairy products are the major food

sources of Ca in the US diet, supplying about

61% of Ca intake; other food groups such

as vegetables, fruits, legumes, nuts, and cereal products contribute most of the rest (4). Meat, poultry, and fish supply very small amounts of

Ca (12). In fact, it is almost impossible to

supply the daily Ca requirement without dairy products in our diet because most other food groups are low in Ca content (Table 1). To equal the amount of Ca (1200 mg) in .946 L (1 qt) of milk, it is estimated that it would take

1.58 kg (7 c) of cooked spinach, 5.2 kg (23 c)

of carrots, 7.25 kg (32 c) of green peas, 22 oranges, 50 tomatoes, or 50 slices of whole wheat bread.

Bioavailability and Absorption of Calcium

Not only is the amount of Ca intake im-

portant but also its bioavailability and ab- sorption by the body. The Ca in dairy products is bioavailable and readily absorbed. Vitamin D is the major regulator of intestinal Ca absorption.

Vitamin D and lactose, which are present in

dairy products, enhance Ca absorption in the body. Certain dietary compounds in other food groups decrease Ca bioavailability. Some vegetables, which on chemical analysis show appreciable amounts of Ca, contain oxalates (e.g., spinach, beet grains, rhubarb) or phytates (e.g., unmilled cereals), which tie up the Ca as

Ca oxalate or Ca phytate, which are insoluble

compounds, so that Ca is very poorly absorbed by the body. Also, high amounts of fiber have been reported to decrease Ca absorption (3).

Middle-aged and elderly persons in general

and postmenopausal women in particular show reduced ability to absorb Ca. Other physio- logical conditions such as vitamin D deficiency, pregnancy, lactation, and certain diseases affect

Ca uptake by the body. Pregnancy and lactation

increase Ca absorption, whereas vitamin D deficiency and certain diseases decrease Ca absorption (3).

Osteoporosis

Recent developments in osteoporosis (the

problem of brittle bones) have indicated that decreased Ca intake is a major cause of this condition (9, 15). Osteoporosis is the most common metabolic bone disease. It is a con-

Journal of Dairy Science Vol. 70, No. 2, 1987

SYMPOSIUM: HEALTH RELATED ASPECTS OF MILK AND MILK PRODUCTS 409 dition of the skeleton in which the amount and strength of bone tissue has been decreased.

Reduction in mass and density of affected

bones makes them weak, "porous" (thus the name of the disease), and susceptible to fracture. The bones usually affected first are those of the spine. Thinned by the disease, these are compressed by the weight of the body resulting in low back pain, back deformity, loss of height, and low capacity for physical activity. Eventually the weakened bone fractures. Other bones also may become involved, particularly those of the pelvis, legs, and arms (15).

The disease is usually not detected early,

because it develops gradually and insidiously. It does not have any distinctive laboratory or clinical signs, and thus diagnosis of this disorder depends largely on special techniques (radio- grammetry, photon absorptiometry, x-ray pho- todensitometry, and computerized tomography) to measure decreased bone mass (9).

It has been estimated that some degree of

TABLE 1. Sources of calcium in commonly used foods (edible portions) compared with dairy products (6).

Foods Amount Ca

Dairy products (mg)

Milk 3.5% fat 236 ml (1 c) 1 291

Low fat, milk 2% fat 236 ml (1 c) 297

Low fat milk, 1% fat 236 ml (1 c) 300

Skim milk 236 ml (1 c) 302

Buttermilk 236 ml (1 c) 285

Yogurt, plain 227 g (8 oz) 274

Swiss cheese 28 g (1 oz slice) 272

Cheddar cheese 28 g (1 oz slice) 204

Ice cream 236 ml (1 c) 116

Cottage cheese, low fat 236 ml (1 c) 155

Vegetables

Spinach, cooked 227 g (1 c) 167

Broccoli, boiled, chopped 227 g (1 c) 137

Carrots, boiled, sliced 227 g (1 c) 51

Cabbage, fresh, cooked 227 g (1 c) 44

Green peas, boiled 227 g (1 c) 37

Lettuce, leaf 2 large leaves 34

Tomato, whole 1 24

Potato, baked 1 medium 8

Corn, boiled 227 g (1 c) 2

Meats, Poultry, Fish

Sardines with bones 85 g (3 oz) 372

Salmon, canned 85 g (3 oz) 167

Egg, whole without shell 1 27

Chicken, fried 1 breast 18

Hamburger, broiled 85 g (3 oz) 10

Steak, broiled 85 g (3 oz) 9

Tuna, canned 85 g (3 oz) 7

Fruits and Nuts

Orange, fresh 1 54

Peanuts, roasted 14 g (½ c) 53

Raisins 14 g (1~ c) 45

Pecans, halves 14 g (½ c) 40

Orange juice 236 ml (1 c) 27

Banana, raw 1 10

Peanut butter 14 g (1 tbsp) 9

Cereals

Bran flakes, with raisins 236 ml (1 c) 28

Bread, whole wheat 1 slice 24

Bread, white 1 slice 22

t8oz.

Journal of Dairy Science Vol. 70, No. 2, 1987

410 RUSOFF

osteoporosis affects 15 to 20 million middle-aged and elderly persons, especially postmenopausal women. About one in four women over 60 yr of age are afflicted with this disease (9, 15).

Osteoporosis has been called a multifaced

disease, due to a combination of factors, mainly nutritional, hormonal, and level of physical activity. In addition to low Ca intake, the decline in the production of sex hormones in postmenopause, and lack of physical activity have been found to be involved in bone loss.

Other factors reported to be involved are

heredity, race, smoking, and age (9, 15).

Bone is not a static depot of minerals but

rather, it is in a dynamic state. Throughout life, bone remodeling occurs and new bone is deposited and existing bone resorbed. Peak bone mass is obtained up to 30 to 40 yr of age after which skeleton bone resorption exceeds formation and continues throughout life. Thus, as one ages, there is a negative balance of Ca in the skeleton bone (9). It is therefore imperative that adequate Ca intake is maintained not only during the growing period but also continued during peak bone mass production and on into old age.

Calcium Intake in the US

Over the years, government surveys have

reported that a large segment of the US popula- tion is not consuming the RDA for Ca on any given day (1, 5, 9, 10, 19). The most recent survey carried out by the US Public Health

Service, and known as HANES II (Second

National Health and Nutrition Examination

Survey, 1976 to 1980), substantiates data from previous surveys. The HANES II Ca intake data for all ages was obtained by 24-h dietary recalls of over 20,000 persons as representative of the

US civilian noninstitutionalized population, 1

to 74 yr of age (5).

Table 2 and Figures 2 and 3 present the

HANES II Ca intakes for men and women

compared with the RDA for Ca. It can be seen that the typical US male consumes almost twice as much Ca as the US female of the same age with intakes above or close to meeting the

RDA, except those of age 65 and older. In

sharp contrast, females 11 yr of age and older have Ca intakes much below the RDA. Heany et al. (9) analyzed data from HANES I and II and from USDA and reported that from age 18 to 35, during peak bone mass development, 60 to 70% of US males ingest Ca intakes above the

RDA whereas more than 66% of all US females

do not consume the RDA on any given day, and after age 35, more than 75% fail to ingest the RDA. No wonder about 15 million women suffer with some degree of osteoporosis and fractures. Men also experience osteroporosis but at a much later age than women because of their greater peak bone mass and slower rate of bone loss.

As pointed out previously, effective Ca

absorption by the body is a complex process and concerns not only dietary Ca content but also bioavailability, absorption efficiency, vitamin D intake, interaction of nutrients, and hormonal activity.

Current research and the HANES II data

indicate that continuous consumption of foods rich in bioavailable Ca throughout life is of value in development of peak adult bone

TABLE 2. Daily calcium intake (mg) for males and females by age in the United States population, 1976-1980,

compared with recommended dietary allowances (RDA) (5, 7).

Age, yr

1--10 11--18 19--35 35--64 65--74

RDA 800 1200 800 800 800

Ca intake Males

Mean 955 1254 1091 834 698

Median 889 1100 903 711 597 Females

Mean 866 800 657 580 542

Median 800 707 550 485 475

Journal of Dairy Science Vol. 70, No. 2, 1987

SYMPOSIUM: HEALTH RELATED ASPECTS OF MILK AND MILK PRODUCTS 411 1400
1300
1200
1100
-~1000

¢' 900

.~ 800 ~ 700 ~ 6oo 50~

400 ......... Median

----- RDA 7.~-~

35 ~I~ ~S~7

Age

Figure 2. Daily calcium intake (mg) for males in the United States population, 1976 to 1980, compared

with the recommended dietary allowances (RDA) (5, 7). Graph courtesy of National Dairy Council. 1400
1300
1200
1100
~ 9~ ~ 800 700;

0 600~

500-
400-

0 [ I ........ ~:;rao

I I ---- ROA I

,2 I 5~ 1,2~,, r ,8~ .... '.3, ' ' ' ' 6S-74 55-64 35-~ 4554 3.5 9-11 15.17 Age

Figure 3. Daily calcium intake (mg) for females

in the United States population, 1976 to 1980, compared with the recommended dietary allowances (RDA) (5, 7). Graph courtesy of National Dairy Council. mass and possibly a reduction in osteoporosis and bone fracture suscepetibility.

Milk and dairy products, the best food

sources of bioavailable Ca, are vital in daily diet to maintain a good skeleton into old age.

Calcium and Hypertension

High blood pressure is one of the major risk

factors linked to cardiovascular disease. It is considered a major health problem and the principal cause of morbidity and mortality in the US (11). The etiology of most hypertension is unknown, but many factors are involved and contribute to high blood pressure. Genetics, race, age, obesity, smoking, stress, alcohol, and certain dietary components have been implicated as risk factors. The role of Ca as an important factor in controlling hypertension recently has received increasing attention. Several studies have reported an inverse association between dietary

Ca intake and blood pressure (2, 8, 13, 14).

In 1982, McCarron et al. (13) reported

significantly less Ca intake (668 +- 55 mg) in 46 untreated hypertensives (HTN) compared with

Ca intake of 886 -+ 89 mg of 44 normotensives

(NL) controls.

The subjects (average 40 yr of age) in this

study were asked to provide a 24-h dietary intake without being given the purpose of the recall. Main sources of dietary Ca were milk and dairy products. Both groups ingested similar amounts of Ca from milk and nondairy foods with approximately 250 mg Ca being supplied by milk. The main difference in Ca intake between the two groups was the consumption of dairy products other than milk. The diet of the HTN provided only 148 + 34 mg Ca from dairy products other than milk while 400 + 78 mg Ca were provided in the diet of the NL group (median HTN, 21 mg vs. NL, 225 rag,

P<.01). Intake of other nutrients (Na, K,

protein, carbohydrates, fat, and total calories) was very similar for both groups. Although Na and K have been linked with hypertension, the investigators in this study suggested that low Ca intake may be an unrecognized factor in the development of high blood pressure.

Ackley et al. (2) studied the relationship of

dairy products and Ca intake to blood pressure levels in an adult, predominately white upper middle class community in Southern California.

Between 1972 and 1974, 82% of adults (5050

men and women) in the community participated in a survey for heart disease risk factors as part of a Lipid Research Clinic prevalence study.

Consumption of whole milk, lowfat, and nonfat

milk, cream, cheese, and frozen dairy products was converted to milligrams of Ca intake.

Analysis of whole milk and blood pressure data

showed significantly less Ca intake from milk in

HTN vs. NL men (not women). After adjust-

ment for age, obesity, and alcohol consumption, systolic blood pressure was negatively andquotesdbs_dbs27.pdfusesText_33

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