It has been found that the sense of taste and smell become dull as we get older because taste-buds and the nerves involved in the olfactory system deteriorate and die. The number of functional taste-buds may dwindle from about 7000 at birth to 1000 or 2000 by late adulthood. As a result, a 70-years-old may need two teaspoons of sugar in a cup of coffee in order to perceive the same preferred degree of sweetness that was enjoyed from one teaspoonful at age 25. Sensitivity also appears to very with the time of day. Both senses become most acute at about 3 a.m., swing back to a low point around waking time, and then gradually grow sharper again throughout the day.