Medeiros, Lilian C. da Silva*; Lederman, Henrique M.†; de Morais, Mauro B.‡
Osteoporosis is one of the most prevalent illnesses among elderly adults, constituting a public health problem (1). The bone mass formed during the first 2 decades of life and the bone loss index during the aging process influence its occurrence. The recommended primary prevention of osteoporosis, therefore, is an adequate gain of bone mass during infancy and adolescence (1,2).
The formation of bone mass undergoes interference primarily from genetic factors, notwithstanding environmental factors, including nutrition, and exercise also has an effect upon this process (1). Within the nutritional aspects, one of the recommendations is the adequate calcium intake during infancy and adolescence to optimize the gain in bone mass (1,2).
Dairy products are important dietary sources of calcium (3). These foodstuffs also contain lactose, the carbohydrate of milk, which is not absorbed in its intact form, its hydrolysis into glucose and galactose by way of the action of the lactase enzyme being necessary. The level of activity of this enzyme is elevated until the weaning stage and declines with advancing age, a phenomenon called adult-type hypolactasia (4).
Adult-type hypolactasia can produce lactose malabsorption, which is detected by examinations that indicate that this carbohydrate was not digested and therefore was not absorbed, and lactose intolerance, which is characterized by symptoms such as diarrhea, abdominal distension, flatulence, cramps, and abdominal pain after the intake of this carbohydrate (4).
The influence of lactose malabsorption and intolerance on the intake of dairy products and calcium, as well as its possible consequences for bone health, has been investigated. A greater prevalence of lactose malabsorption has been observed in women with osteoporosis when compared with controls (5–7), although other researchers have found conflicting results (8,9). Lower bone mass (10,11) and a greater risk of fractures (12) caused by the restriction of the consumption of dairy products and lower calcium intake have been related to lactose malabsorption and intolerance; however, some studies have not found this association (8,13–15). There is a shortage of data in the pediatric age group; the only study that involved adolescents did not detect any association among lactose malabsorption, calcium intake, and bone mineral content (16).
Given that infancy and adolescence are critical periods for the acquisition of bone mass and that lactose malabsorption could represent a risk factor for lower calcium intake, the objective of present study was to evaluate the calcium intake and bone mass of children and early adolescents in accordance with their absorption capacity to lactose.
PATIENTS AND METHODS
This was a transversal study involving a convenience sample composed of children and early adolescents residing in Sao Paulo, Brazil. To obtain volunteers, the research was announced in the media (newspapers and the Internet), as well as in talks given in district schools and community centers. The data were collected during the period June 2007 through March 2008.
The study had 5 inclusion criteria for participants:
1. Chronological age ≥5 years
2. Absence of diarrhea during the 4 previous weeks
3. Nonuse of antibiotics, laxatives, or enema during the 4 previous weeks
4. Nonuse of medication that affects bone metabolism or calcium supplements
5. Informed consent from the parents of the child's or adolescent's participating in the study
The sample size was calculated based upon the study by Di Stefano et al (11), carried out in Italy, in which men (n = 44) and women (n = 59), average age 28 years (range 25–33 years), were evaluated. In the Di Stefano et al study, a statistically significant difference was detected in the z score of the bone mineral density of the lumbar spine (L2–L4) between lactose malabsorbers and intolerants (−0.78 ± 0.7) and lactose malabsorbers and tolerants (0.12 ± 0.6). To this end, considering this difference of 0.66, standard deviation of 0.70, power of 80%, and α risk of 2%, the sample size was estimated at 24 individuals with lactose malabsorption and intolerance and 24 with lactose malabsorption and tolerance. The research was reviewed and approved by the research ethics committee of the Federal University of Sao Paulo (UNIFESP).
Weight and height were measured in accordance with the Jellife recommendations (17). Weight was obtained using a portable electronic balance of 150-kg capacity and 100-g scale. An inelastic tape fixed to the wall without a baseboard and a wooden L-shaped instrument angled at 90° to assist in the reading were used to measure height.
To evaluate the nutritional state, the anthropometric indicators of weight-for-age, height-for-age, and body mass index (BMI = weight [kg]/height [m2]), expressed in z score, were calculated. The calculations were carried out with the help of the EpiInfo program, version 3.4.3 (Centers for Disease Control and Prevention, Atlanta, GA).
Hydrogen Breath Test
The parents of the child or early adolescent were advised in the examination preparation. On the evening before the test, the child or early adolescent was fed a meal of white rice and ground-up chicken, fried or roasted (18), and was required to fast after this meal (19), to avoid a falsely elevated hydrogen reading in the base sample (fasting). Before the start of the test, oral hygiene was carried out using an antiseptic mouthwash to prevent the production of hydrogen by oral flora (20).
The hydrogen breath test lasted 180 minutes and collected 9 air samples; the first sample was taken during fasting and the others were taken after 15, 30, 45, 60, 90, 120, 150, and 180 minutes (21). The participants did not eat any food or do any physical exercise and they did not sleep during the test, so as not to alter the excretion of hydrogen (22,23).
After the collection of the first sample (fasting), a 20% aqueous solution of monohydrated lactose was administered in a dose of 2 g/kg of body weight up to a maximum of 50 g (4).
The air collection was carried out using a “no rebreathing valve set up” device (Quintron Instrument Co, Menomonee Falls, WI). The air samples were stored under refrigeration for a maximum of 24 hours and analyzed using a Quintron Microlyser gas chromatogram (model 12i).
Delta hydrogen values (ΔH2) were calculated, which is the difference between the maximum hydrogen value in a sample and the baseline value. Each participant was questioned for the presence of symptoms during the test and in the 24 hours afterward before revealing the examination result to their parents.
In an attempt to detect false results, the participants who did not produce hydrogen in the lactose test were submitted to a new respiratory test, with a minimum interval of 3 days between each, using the same methodology with the exception of the substrate, which was a 10% aqueous solution of lactulose in a 10-g dose. Individuals with an increase of hydrogen in expired air relative to their fasting result <10 ppm were classified as nonhydrogen producers (24) and were excluded from the study.
Lactose malabsorption was defined as ΔH2 values ≥20 ppm in the lactose test (25). Lactose absorption was defined as ΔH2 values <20 ppm in the lactose test and ≥10 ppm in the lactulose test (24). Lactose intolerance was defined as the presence of ≥1 gastrointestinal symptoms in response to lactose administered for the realization of the breath test (4).
The responsible adults were questioned about whether the child or early adolescent had presented milk intolerance, characterized by the presence of gastrointestinal symptoms after the ingestion of milk in their day-to-day routine.
Two 24-hour recalls were applied—1 for weekends and 1 for weekdays, which were nonconsecutive—with the objective of estimating the food intake of the children or adolescents (26). The calculations were made in the computer program Support System from Nutritional Decision, version 1.5 (Health Informatics Center, Federal University of São Paulo). Information not available through the program was compiled from labels and tables of the food's composition. The daily intake of energy (kilocalories), proteins (grams), carbohydrates (grams), lipids (grams), total calcium (milligrams; considering all of the dietary food), calcium obtained from milk (milligrams), milk (milliliters), cheese (grams), yogurt (milliliters), ice cream (grams), and calcium density of the diet (milligrams/1000 kcal) were determined. The calcium density of the diet was calculated based upon the formula
Equation (Uncited)Image Tools
The calcium intake was compared with the reference value, namely adequate intake (AI) of the dietary reference intakes. In the age groups 5 to 8 years and 9 to 12 years, the reference standards are 800 and 1300 mg/day, respectively (27).
A dual-energy x-ray absorptiometry was used to determine bone mineral density and bone mineral content. The examinations were carried out at the Image Diagnostics Center of the Oncology Pediatric Institute (IOP-GRAACC, São Paulo, Brazil). DPX-IQ Lunar equipment was used (Lunar Radiation Corp, Madison, WI). The densitometry software used as a reference the North American pediatric population involving all ethnic groups (NHANES/EUA data). The bone region analyzed was the lumbar spine (L2–L4); the following data were obtained: bone mineral content, bone mineral density, and z score of bone mineral density.
Parametric and nonparametric statistical tests were used depending upon the nature of the studied variables. For proportions comparisons, the Fisher exact test and the χ2 test were applied. The comparisons between continuous variables were carried out using the Mann-Whitney rank sum test and the t test. The Spearman correlation test was applied to analyze the relation between calcium intake and the z score of bone mineral density. The calculations were made in Jandel Sigma Stat 3.5 (Systat Software, Point Richmond, CA) and EpiInfo version 3.4.3 programs. The level for rejection of the null hypothesis was set at <0.05.
Eighty-six children and early adolescents were subjected to the hydrogen breath test using lactose, 4 of whom were excluded for missing the test with lactulose for diagnostic confirmation. Of the remaining 82 subjects, 6 (7.3%) were excluded for not being hydrogen producers after the test with lactulose. A final total of 76 individuals were included in the study. The participants’ ages varied between 5 and 12 years; with respect to race, 67.1% (51/76) were white and 32.9% (25/76) were African/mixed origin.
The prevalence toward lactose malabsorption was 61.8% (47/76), being that among these malabsorbers, some 53.1% (25/47) showed intolerance to the lactose administered during the respiratory test. In this group of lactose malabsorbers and intolerants (n = 25), the following symptoms were reported: borborygmy (20.0%), flatulence (28.0%), abdominal pain (72.0%), and diarrhea (96.0%). Diarrhea was defined as decrease in the consistency of stool (greater looseness of stool) accompanied or not with an increase in the frequency of evacuations.
The participants were divided into 2 groups for the results presentation: lactose malabsorbers (n = 47) and lactose absorbers (n = 29). There was no statistically significant difference between malabsorbers and absorbers with regard to either sex or age. There was a higher frequency of lactose malabsorption among African/mixed origin participants when compared with whites. An earlier history of milk intolerance was reported by 3 participants, all of whom were diagnosed as having lactose malabsorption (Table 1).
We verified that none of the participants had made use of any type of vitamin or minerals supplements. The type of milk ingested by the lactose malabsorbers and lactose absorbers was whole milk with the normal level of lactose; none of the participants made use of Lactaid milk. The daily intake of energy, proteins, carbohydrates, lipids, total calcium, milk calcium, milk, cheese, yogurt, and ice cream, and the calcium density of the diet did not significantly differ between lactose malabsorbers and lactose absorbers (Table 2).
In relation to the anthropometric data, a statistically significant difference was not detected in the comparison of weight, height, z score of weight-to-age, z score of height-to-age, BMI (kilogram per square meter), or the BMI z score, according to the lactose absorption capacity (Table 3).
The bone mineral content, the bone mineral density, and the z score of the bone mineral density of the lumbar spine did not differ between lactose absorbers and lactose malabsorbers (Table 4).
To evaluate whether there had been a difference among the groups in relation to race, a new analysis on total calcium intake and bone mineral density of the lumbar spine (L2–L4) was carried out in accordance with the diagnosis (lactose malabsorbers and lactose absorbers) and race (white and African/mixed origin), which did not point to any significant difference between the groups (data not presented).
Because some studies suggest that individuals with malabsorption associated with intolerance to lactose administered in the hydrogen breath test presented a lower calcium intake and alterations in their bone mass, an additional analysis of the data was carried, taking into consideration the presence of intolerance to lactose administered in the test. No significant difference was observed among the lactose malabsorber intolerants, lactose malabsorber tolerants, and lactose absorbers (data not presented).
It was observed that in all of the age groups, the median calcium intake was lower than the AI of the dietary reference intakes (Table 5). The comparison between individual calcium intake and the AI of 800 mg/day, for the 5 to 8 years group and 1300 mg/day for the 9 to 12 years group, found that 77.7% of the children ages 0 to 8 years and 96.8% of those ages between 9 and 12 years did not ingest the recommended calcium quantity.
On directly analyzing the relation between calcium intake and the z score of bone mineral density of the participants in the present study, no significant correlation was verified (Spearman correlation test).
The major proportion in the studies that have investigated the association among lactose malabsorption, calcium intake, and bone mass have been carried out on an adult and elderly population (8,10,12–15). Only a few research studies have involved young adults (11) and adolescents (16).
In the present study, the hydrogen breath test was used for the diagnosis of lactose malabsorption. The dose was used with the intention of identifying the true number of children and early adolescents with adult-type hypolactasia, taking into account that the use of lower doses of lactose could well underestimate its prevalence (28). The prevalence toward lactose malabsorption varies from 0% to 30% in the northern and central European populations and from 60% to 100% among indigenous, Latin Americans, Asiatic, and African populations (29), data confirmed within the present study that detected a high prevalence toward lactose malabsorption (61.8%), with a significantly greater frequency among African/mixed origin.
The capacity for lactose absorption, together with the occurrence of symptoms after the administration of the lactose in the test (lactose intolerance), was also evaluated to verify whether the individuals with this complaint could alter their food intake, principally in relation to milk.
The dietary analysis did not reveal a statistically significant difference in relation to intake of energy, proteins, carbohydrates, and lipids between lactose absorbers and malabsorbers, even when considering the presence of lactose intolerance in this latter group. This same result has also been observed in other research studies (30,31).
Furthermore, the daily intake of total calcium, milk calcium, milk, cheese, yogurt, ice cream, and the calcium density of the diet (milligrams of calcium/1000 kcal) did not differ between lactose absorbers and malabsorbers, even when considering the presence of lactose intolerance in the latter group. These results are, in part, in agreement with the literature, given that differences in relation to the calcium intake between lactose absorbers and malabsorbers evaluated by the hydrogen breath test were not detected (10,11,13,14,16,30). This indicates that lactose malabsorption by itself does not represent a risk factor for the reduced milk product intake. Some studies have found a calcium intake significantly lower in the malabsorbers with symptoms of intolerance to the lactose administered during the test when compared with lactose malabsorber tolerants and the absorbers (10,11,30,32), a fact not confirmed in the present research.
There was no association between lactose malabsorption and a reduction in milk, dairy products, and calcium intake among the children and early adolescents evaluated, even when considering the presence of lactose intolerance to a load lactose administered in the breath test. In fact, the behavior of the individuals diagnosed as having lactose malabsorption in relation to the milk and dairy products intake is variable. The occurrence of the symptoms depends on factors such as the quantity and form of lactose consumption, rate of gastric emptying and intestinal passage, residual level of lactase enzyme activity, and the properties of the colonic microflora (32–34).
Studies have demonstrated that the lactose contained in 250 mL of milk (12.5 g) can be well tolerated by malabsorbers intolerant to larger quantities of lactose in single doses (35–37). The concomitant consumption of milk and other foods slows gastric emptying, bringing about the gradual passage of lactose to the small intestine and favoring the action of the lactase enzyme in the hydrolysis of lactose (38,39). In the present study, the lactose malabsorbers presented a median milk intake of 225 mL/day, which corresponds to 11.25 g of lactose. The habitual low lactose intake could underestimate the role of lactose malabsorption over the calcium intake, given that the probability of the occurrence of the symptoms after the milk and dairy product intake becomes reduced (40). The average z scores for weight/age, height/age, and BMI were not statistically different according to the lactose absorption capacity.
The data obtained in the bone densitometry examination did not indicate any statistically significant difference between lactose absorbers and malabsorbers (tolerant or intolerant) with respect to their bone mineral content, bone mineral density, and the z score of the bone mineral density of the lumbar spine.
Thus, children and early adolescents in this population with lactose malabsorption did not have lower bone densities, bone mineral content, or calcium intakes, even when considering the presence of lactose intolerance. It should be emphasized that the role of malabsorption and of lactose intolerance, as well as the low consumption of calcium during the period of greatest bone mass increase, that is to say, between 11 and 14 years for girls and 13 and 17 years for boys (41), was not evaluated in the present study because the individuals involved did not fall into these age groups. The only study that involved adolescents (10- to 13-year-old girls) did not detect an association among lactose malabsorption, lower calcium intake, and alterations in the bone mineral content (16). Because it was transversal, the present study did not evaluate the effect of lactose malabsorption during a long period of time, but nevertheless, research involving young Italian adults of both sexes (average age 28 ± 2 years) observed lower calcium intake and lower bone mineral content of the femoral neck and lumbar spine in the malabsorbers who presented intolerance toward lactose administered in the hydrogen breath test as compared with the malabsorbers with lactose tolerance as well as with the absorbers (11). This suggests that these individuals could well have restricted their milk and calcium intake for a long period of time, thus affecting their gain of bone mass. These findings concur with another Italian study that involved postmenopausal women and detected that the malabsorbers with intolerance to lactose administered during the hydrogen breath test ingested less calcium and presented a lower z score of the bone mineral density for the lumbar spine than the malabsorbers without intolerance (10).
Another important point that deals with the consumption of milk and calcium is intolerance to milk, that is to say, the perception of symptoms after the ingestion of this food on a day-to-day basis. A North American study compared adolescents with and without perceived milk intolerance (data obtained by questionnaire) and the study revealed a significant reduction in the consumption of total calcium, as well as the calcium of dairy products and milk in girls with self-reporting perceived milk intolerance when compared with those adolescents without perceived milk intolerance. The bone mineral content of the spine (L2–L4) was significantly lower in the girls with perceived milk intolerance in relation to the girls without perceived milk intolerance. These results suggest that perceived milk intolerance is associated with a reduction in milk, dairy products, and calcium intake and with lower bone mineral content in adolescents (16). In the present study, the frequency of milk intolerance complaints in the sample was small, only 3 individuals. The group reported a daily intake of milk and calcium that was extremely low (an average of 27.50 ± 47.63 mL of milk and 338.53 ± 62.28 mg of total calcium), indicating a restriction, or even exclusion, of milk in their diet as a consequence of the symptoms after eating the food. In relation to bone mass, the z score values of bone mineral density of the lumbar spine shown by these individuals varied from −1.7 to 1.0, no z score ≤−2.0 having occurred, which would indicate low bone mineral density for their chronological age (42). Because of the small number of children in our study with these conditions, it was not possible to perform an analysis based on perceived milk intolerance.
It is worth mentioning that, independent of the capacity of lactose absorption, the ingestion of milk and dairy products by the participants was low, a result similar to that observed in another study, which involved Brazilian adolescents (43). In a comparison between Brazil and other countries of milk consumption in 2009, it was verified that the quantity per capita ingested was similar to that of Germany, France, and Italy, but reached less than half the quantity ingested in Finland; furthermore, if the per capita cheese were considered, the consumption in Brazil is almost 7 times lower than in the cited countries (44). To this end, it was verified that the eating standard of Brazilians in relation to dairy products could contribute to a low calcium intake, which was confirmed in the present study, within which it was observed that the greater part of the children and early adolescents presented calcium intake lower than the recommendation. This low ingestion also occurred in other Brazilian studies involving populations of children (43,45) and adults (46,47). On directly analyzing the relation between calcium intake and the z score of bone mineral density of the participants in the present study, no significant correlation was verified, a result similar to that obtained in another study involving Brazilian adolescents with low calcium intake (45). Consequently, studies that evaluate both Brazilian children's and adolescents’ bone mass involving different levels of calcium intake are necessary.
Future studies must involve children and adolescents who effectively restrict or exclude milk and other dairy products from their diet regardless of whether their conduct is associated with lactose malabsorption and intolerance. The degree of reduction of calcium intake in this group and the possible consequences on bone mass need to be evaluated.
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