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In China, there is a tendency to avoid milk products, because most Chinese peopl e dislike the taste and the gastrointestinal symptoms associated with milk, even though they know milk is an important food. A high incidence of lactase defic iency (LD) has been reported in Asian and African populations,［1］but there ar e still no exact figures to evaluate the tolerance to lactose or variations in l actase activity in different age groups among the Chinese population in China.
The aim of this study was to determine lactose metabolism and lactase activity in Chinese children of different ages, and to assess the relationship between l actase deficiency and milk tolerance. The results may be helpful for nutrition programs and can be used to encourage milk consumption in the various age groups of the population.
METHODS
Subjects
Beijing, Harbin, Shanghai, and Guangzhou were selected as the study regions. They represent the northern and southern areas of China.
A total of 1200 children were recruited from nursery, primary and secondary sc hools in the four cities. Four hundred children were recruited from each of the following age groups: 3-4 years, 7-8 years and 11-13 years groups. The recruit ment of the students started in September 1997. Data collection began in Octobe r and was completed in December 1997. 1168 subjects were selected according to the following criteria: no diarrhea, chronic constipation or other gastrointesti nal problems during the test period; no use of any drugs for one week prior to t he test; good general health without signs or symptoms of acute or chronic illne ss; parents of the children were natives of the selected cities.
Materials
Lactose was provided by AMPC, IUC, USA. Milk powder was produced in Hongxing Dairy Products Factory in Harbin (lactose content of 260-280 mg/100 g). Sta ndard hydrogen (50 ppm and 30 ppm) was produced in the Center of Standard Subs tance, Beijing, China. Tubes for collecting gas was produced by Labco Limited H igh Wycombe, England.
Methods
Interview
Detailed milk-drinking habits and infant feeding history of the children were recorded on a questionaire. Each child and his parents were asked whether they d rank milk every day and if they had any bloating, pain or diarrhea after consumi ng milk products, and which dairy products they liked.
General physical examination
All the subjects had a physical examination by a local pediatrician before th e test day. The examinations included weight, height and a basic physical exam (no lab) with health history to exclude suspected cases of digestive system disease.
Lactose tolerance test
After written informed consents were obtained from the parents of the childre n, interviews and physical exams were done before the lactose intolerance test. Subjects fasted overnight for 12 hours and arrived at school at 7 o'clock in th e morning. A baseline alveolar expiratory sample was taken. Within 5 minutes, each subject ingested lactose 25 g/200 ml water under strict supervision, afte r which they had 15 minutes rest.［2］
During the test period, the child had to be at ease. They played cards or li stened to a story. They were allowed to drink water only. Breath samples were collected by the end-expiratory technique at 0, 30, 60, 120 and 180 min after ingestion. The occurrences of symptoms (such as colicky pain, abdominal distent ion with flatulence and diarrhea) were recorded for 8 hours under strict supervi sion.［3］
Milk tolerance test
Any child who had an expired hydrogen rise of >20 ppm was defined as ha ving lactase deficiency (LD). The subject who was diagnosed as a lactase defici ency individual was given the milk tolerance test every three days. Fifty grams of milk powder with 13-14 g lactose in 200 ml water were given under the same conditions as the lactose tolerance test.
H 2 analysis
Breath samples were analyzed for hydrogen concentrations by micro-hydrogen g as chromatography, and a standard substance was used to correct each result.
Statistical analysis
Data were expressed as mean ±s. The statistical significance of the re sults was assessed by two-way analysis of variance, Chi-square test, or regres sion analysis, as appropriate. Probabilities of <0.05 were considered signific ant. Calculations were done using SAS software.
Criteria
Lactase deficiency was defined by an expirate-hydrogen rise of >20 ppm afte r a test meal of 25 g lactose or 50 g milk powder. Lactose intolerance was de fined by the presence of two or more clinical symptoms and signs after ingestion of 25 g lactose or 50 g milk powder during the test period.［4］
RESULTS
General information of subjects
The general information about subjects is summarized in Table 1 . And the fee ding history, milk product intake, frequency and the preferred milk products for each age group are provided in Tables 2 and 3.
The prevalence of lactase deficiency and lactose intolerance
One important finding was that lactase deficiency was very common among Chines e children. Lactase activity decreased with age. The subjects showed a deficie ncy at the age of 7-8 and 11-13 ( Table 4 ).
Clinical signs were recorded for an 8 hour period.The children often complained of discomfort after drinking 25 g lactose.The symptoms occurred most frequently between 60 to 180 min after ingestion ( Table 5 ).Significant differences in lactose intolerance were found between northern and southern cities ( Table 6 ).It was suggested that lactose intolerance is a reason that Chinese children complain about milk products.
Milk intolerance
When children had an intake of 50 gram milk powder with 13-14 g lactose, the intolerance symptoms decreased significantly. Among 3-5 year old children , 11.7% had an expired hydrogen level of H 2 >20 ppm, but children of 7-13 y ear old have higher level ( Table 7 ).
DISCUSSION
Lactase deficiency
Digestibility of lactose can be measured by the rise of expired hydrogen. Weste rn countries often use 50 g lactose (equivalent to 1000 ml fresh milk) for the lactose tolerance test, but 25 g lactose (equivalent to 500 ml milk) is used among Asian countries because of lower milk consumption in these regions.
Secondary lactase deficiencies are very common in the world, especially in Afric an and Asian races with 75% or more of the population suffering from a deficienc y. The prevalence varies depending on race and age. In north western European countries there is less than 5% prevalence compared to 100% in some parts of Asi a and Africa.［1］ Some studies have shown that secondary or adult la ctase defi ciency occurs at certain ages (6-8 years in Japanese and 1-5 years in African ch ildren).［5］In the present study, lactase deficiency occurred at 7-8 years o f age in the Chinese population. Among the subjects of this group, 87.6% had a high rise in breath hydrogen (>20 ppm) after oral administration of 25 g lact ose. There was no significant rise in the 11-13 year group when compared to th e 7-8 year group. The results show that lactase activity may begin to decrease at age 3-5, and Chinese children show decreased or non-persistent lactase acti vity at age 7-8.
A difference in the prevalence of lactase deficiency in the four cities was o bserved. It seems that there is a higher prevalence (87.7% and 94.9%) in sout hern cities (Guangzhou and Shanghai, respectively), and a lower prevalence (83. 6% and 82.1%) in northern cities (Beijing and Harbin, respectively). Ther e were some similar patterns of results in France (north 10% and south 40%) and Italy (north 30% and south 100%).［6］
Lactose intolerance and clinical symptoms
In this study, 31% of the total subjects at the age of 7-13 were sufferin g f rom lactose intolerance, and 64.3% lactose intolerance subjects had only slight clinical signs such as flatulence, bloating, or gaseousness. 30% lactose intol erance children with excess gas or diarrhea and cramps seemed to have difficulty tolerating 25 g lactose and complained often during the test period. 6% lacto se intolerance children had severe diarrhea and cramps or pain. There was simil ar distribution of frequency for symptoms among the different age groups.
Lactose tolerance and milk tolerance
There was a 50%-80% decrease in breath hydrogen level (BHL) when lactose intoler a nt subjects were fed 50 g milk compared to lactose. There was also the elimina tion of clinical symptoms of maldigestion. The results show that the tolerance reaction was almost equivalent to lactose in milk or lactose alone, and that lac tase activity in Chinese children exists to certain degree, as lactose intoleran t individuals were able to tolerate some lactose. It is recommended that a smal l amount of milk may be better tolerated by all lactase deficient individuals.
REFERENCES
1. Johnson AO, Semenya J, Buchowski, et al. Correlation of lactose maldigest ion, lactose intolerance and milk intolerance. Am J Clin Nutr 1993;57:399-401 .
2. Jia BQ. Breath hydrogen test. Chin J Ped 1987;26:129-130.
3. Ladas SD, Raptis S. Oral dose of lactose to indicate lactose maldigestio n. J Pediatr Ga Nutr 1990;11:489-493.
4. Michele AS, Jose MS, Teri JL, et al. Effect of yogurt on symptoms and kinet ics of hydrogen production in lactose-malabsorbing children. Am J Clin Nutr 1995;62:1003-1006.
5. Meei-yn L, Jack DA, Margaret MC, et al. Comparative effects of exo genous lactase preparations on in vivo lactose digestion. Diges Dis Sci Am J Cl in Nutr 1993:38:2022-2027.
6. Michael V, Schrezenmeir J. Nutritional aspects of lactose. Carbohydrat es 1999:25:18-23.
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