Table 1.

Ten principals of programming

10 principals of programming
During development, there are critical periods of vulnerability to suboptimal conditions. Vulnerable periods occur at different times for different tissues. Cells dividing rapidly are at greatest risk. Factors that increase risk include: Too much of a normal chemical such as a hormone, critical nutrient or vitamin; Deficiency of a normal chemical such as a hormone, critical nutrient or vitamin; Abnormal chemicals such as alcohol or nicotine; Abnormal physical forces, such as high blood pressure	Programming involves several different structural changes in important organs The absolute numbers of cells in the organ may increase or decrease; The relative proportions and distribution of different types of cell within the organ may be unbalanced; The normal blood supply to the organ may not form; Too many or too few hormone receptors may form with a resultant resetting of feedback and other control mechanisms
Programming has permanent effects that alter responses in later life and can modify susceptibility to disease. Changes that occur during development may lie dormant to emerge later in life when exposed to a second, lifestyle hit or when normal life-stage changes such as puberty occur and expose the maladaptive consequences of the programming	Compensation carries a price. In an unfavorable environment, the developing baby makes attempts to compensate for deficiencies. Following compensation, birth weight may be normal or only slightly decreased. However, the compensatory effort carries a price
Fetal development is activity dependent. Normal development is dependent on continuing normal activity. Each phase of development provides the required conditions for subsequent development	Attempts made after birth to reverse the consequences of programming may have their own unwanted consequences. When postnatal conditions prove to be other than those for which the fetus prepared, problems may arise
The placenta plays a key role in programming	Programming often has different effects in males and females
Fetal cellular mechanisms often differ from adult processes. Fetuses react differently to suboptimal conditions than do newborn babies or adults.	The effects of programming may pass across generations by mechanisms that do not involve changes in the genes