The process of turning milk into cheese dates back earlier than 5200 BC.DNA analysis in February 2012 revealed that Ötzi was lactose intolerant, supporting the theory that lactose intolerance was still common at that time, despite the increasing spread of agriculture and dairying.Genetic analysis shows lactase persistence has developed several times in different places independently in an example of convergent evolution. History of research
It is not until relatively recently that medicine recognised the worldwide prevalence of lactose intolerance and its genetic causes. Its symptoms were described as early as Hippocrates (460–370 BC), but until the 1960s, the prevailing assumption was that tolerance was the norm. Intolerance was explained as the result of a milk allergy, intestinal pathogens, or as being psychosomatic – it being recognised that some cultures did not practice dairying, and people from those cultures often reacted badly to consuming milk. Two reasons have been given for this misconception. One was that early research was conducted solely on European-descended populations, which have an unusually low incidence of lactose intolerance and an extensive cultural history of dairying. As a result, researchers wrongly concluded that tolerance was the global norm. Another reason is that lactose intolerance tends to be under-reported: lactose intolerant individuals can tolerate at least some lactose before they show symptoms, and their symptoms differ in severity. The large majority of people are able to digest some quantity of milk, for example in tea or coffee, without developing any adverse effects.
It is best heard at the right upper sternal border (aortic area). It sometimes radiates to the carotid arteries. In mild aortic stenosis, the crescendo-decrescendo is early peaking. Whereas in severe aortic stenosis, the crescendo is late-peaking. In severe cases, obliteration of the S2 heart sound may occur. Stenosis of Bicuspid aortic valve is like the aortic valve stenosis heart murmur. But, one may hear a systolic ejection click after S1 in calcified bicuspid aortic valves. Symptoms tend to present between 40 and 70 years of age. Mitral regurgitation is a holosystolic murmur. One can best hear it at the apex location and it may radiate to the axilla or precordium. When associated with mitral valve prolapse, one may hear a systolic click. In this scenario, valsalva maneuver will decrease left ventricular preload. This will move the murmur onset closer to S1. Isometric handgrip will increase left ventricular afterload. This will increase murmur intensity. In acute severe mitral regurgitation, one may not hear a holosystolic murmur. Pulmonary valve stenosis is a crescendo-decrescendo systolic murmur. One can hear it best at the left upper sternal border. It has association with a systolic ejection click that increases with inspiration. This finding results from an increased venous return to the right side of the heart. Pulmonary stenosis sometimes radiates to the left clavicle. Tricuspid valve regurgitation is a holosystolic murmur. It presents at the left lower sternal border with radiation to the left upper sternal border.