The study of statistics such as births, deaths, income, or the incidence of disease, which illustrate the changing structure of human populations.
Answer: Calcium
Explanation:
The Vitamin D is an important vitamin and it is related with the element calcium in the body. The Vitamin D is responsible for the absoprtion of calcium in the body present in the food. In the deficiency or depletion of the Vitamin D in the body is likely to affect the calcium levels. The calcium is the main element present in the bones and the teeth. Calcium helps to build bones. In the condition which involves the depletion of Vitamin D levels the calcium levels will also deplete. This will result in conditions like oesteoporosis, rickets and other bone deformities.
Thus people in the northern climates receiving low sunlight, will likely to receive low Vitamin D and will likely to develop bone related problems due to low calcium levels.
Some psychotropic medications can result in lucid dreams, it has also been proposed that some forms of fungi can enhance ones capacity to be able to interact with dreams but this is incredibly dangerous in practice. Usually attaining a healthy amount of sleep (8hrs a night) as well as being aroused before you adequately release from NREM sleep, can help you recall a dream.
