Size of the breast is mainly determined by genetics. If we look at the distribution of bra size world wide, we see that most people around the world average around a B cup. People who live near the North Pole, such as Russians, tend to have larger bra sizes. The reason is that they have more fat under the skin as an adaptation to cold climates. People who live in tropical regions tend to have less fat under the skin so the women in those areas tend to have smaller cup sizes. Fat is not good because fat women tend to have a higher chance of getting breatst cancer. If a person has breast cancer then surgery may mean that they will have no breast tissue. So, just take it easy, and let nature take its course. Small breasts have their advantages. Women who have big breasts also tend to have back problems, and gravity also takes its toll. As people get older, their breasts will sag. People with big breasts will see more sagging.