|MadSci Network: Biochemistry|
1. Lactose is a carbohydrate naturally occuring in mother's milk from mammals (in fact mother's milk is probably the only source). In the intestines the lactose should be devided into two parts, glucose and galactose. For this the enzyme lactase is needed.
In the last stage of the pregnancy, the foetus developes lactase activity. This activity still increases after birth. Depending on the species, the time the maximum lactose activity is reached varies. After the maximum the activity decreases and remains at a constant low level. It has been thought for some time that humans were the only species in which the lactase activity did not decrease that dramatically. Studies from 1965-67 showed that in Africa large populations did not have this lactase activity. Now people of Caucasian origin (whites) are thought to have this lactase activity, whereas non-Caucasians do not have the activity.
Some very crude figures showed that in Europe lactose intolerance is present in 0-30% of the population, the US (total) 30-70%, Africa and large parts of China 70-100%.
In the black population of the US, malabsorption occurs indeed in about 70% of the population. From the Netherlands I know that the amount of lactose intolerant people is only a few percent (3-5%), but by increasing immigration this percentages increases.
2. Lactose tolerance is an achievement of humankind, starting somewhere around 4000 years before Christ. Populations who have a relatively high consumption of milk as an important ingredient of the diet have adapted this achievement. Populations where fermented milk is consumed (like ghee in India and youghurt in Turkey) are less in need of lactase, because fermented milk products contain less lactose. In these populations a percentage of 30-70% of lactose intolerance is seen.
3. people need milk or another source of calcium. Some people (like veganists and macro-biotics) decrease or skip the milk consumption and the consumption of other foods from animal origin. Alternative calcium sources can be used. A study among children with a macrobiotics dietary regime showed that these children had stunted growing and that ricketts was more common (so they had bad skeletal development.)
Milk is a good source of calcium. I give you a list with some foods for comparison.
per 100 gram product Cheese 400-1200 mg Milk 120 mg Human milk 35 mg eggs 50-60 vegetables 25-250 mg (green vegetables fall in the lower part) maize 5-18 whole wheat 30-40For Europe and northern America milk provides about half of the daily calcium intake.
From several studies a less good skeletal growth was seen in subjects with low calcium intake. Whether higher calcium intake indeed does increase the bone strength is not certain. Some populations with naturally low calcium intakes do not necessarily have a lower bone mass. A sufficient amount of calcium however is necessary for growing children and pregnant women.
Your questions whether milk can increase your risk of osteoporosis I can't answer. I never have read any studies on that subject.
I hope that I have satisfactory anwered your questions
Lucy van de Vijver
Try the links in the MadSci Library for more information on Biochemistry.