LIFE AHEAD - Its BASIS and METHOD
This section is intended for researchers and others that wish to know details about how Life Ahead was developed. For the usual health-interested person what is included here can be briefly summarized in two paragraphs following:
Abstract: Life Ahead starts with the rates of 11 or 12 key categories of disease and death for an average US population that does not smoke cigarettes. The effect on risk of disease and life of each factor is taken from a difference in an individual's factor vs. that of this average population. For example, if as a man your cholesterol is 250 at an age of 50, your risk of heart disease will be computed as higher than that of the 213 cholesterol of the average male US population at this age If it is 150, your risk will be computed as lower than that of this average level of 213. If you do not enter a factor as say of blood pressure, Life Ahead will assumed as default an average population value. One that smokes cigarettes will have much higher risks than that of this non-smoking population. The program thus compares each of your risks with those at age for this base US population of non-smokers in deriving its overall result.
Life Ahead derives a difference in the probable biochemical processes and rates in which these diseases progress during life, and develops complete new life tables for each year to life expectancy for each factor or for change in a factor from a starting age. A change in risk of one disease will result in changes in the development of all other diseases. Or a starting or stopping of a new habit (as smoking or use of a vitamin) will initiate a steady increase or decrease in risk with its duration of its use. The risks of disease and death computed by Life Ahead should approximate the real values that populations will experience as a result of almost any combination of diet, exercise, or other habits. A caution, however, is that the program only can compute risks of a population. The actual risks of individuals will vary from that of the population due to individual genetics and family related risks that still cannot be valued precisely.
The Life Ahead Base File: Life Ahead initiates with health results for populations of men and women having the death rates of the US population of the mid and later 1990’s. Eleven categories of death for men and twelve for women are included, three for cardiovascular diseases as Coronary Heart Disease, Other Heart Diseases and Stroke; five or six for cancer as Breast (for women only), Lung, Genital (Prostate for men, all genital for Women), Colorectal, Lung and All other Cancer; and categories of All other Diseases; Motor Vehicles; and Other Non-disease including accidents. The present Life Ahead model considers effects of habits and factors primarily for the cardiovascular diseases and cancer, and does not attempt to consider the effect of habit changes on All other Diseases or Non-disease deaths for other than effects of alcohol.
Actual data by disease were available from the US National Health Statistics (NIH) to about age 93. Death rates for this population were extended and interpolated to annual values by year from age 1 to age 110. This primary model was adjusted to be consistent with survival rates and life expectancy from ages 50 to 100 as given in the US vital statistics. But because of lack of data at higher ages it was necessary to extrapolate estimates of death rates by disease at the higher ages. But values for these higher ages are used only for individuals of advanced present age.
Available NIH statistics are for populations of men and women that smoked differing amounts of cigarettes at various ages. Thus an adjusted model was developed by subtracting out the probable deaths due to smoking for each disease category. (See Smoking in the Health Research Library). NIH data for the percentages of US men and women that smoked, and for the number of cigarettes they smoked in each age and sex category were used in this adjustment. Thus the primary set of death rate statistics used in Life Ahead is that of non-smoking fairly contemporary all US populations of men and women. Starting from this non-smoking basis, the risk of any smoking individual can be readily computed.
Although primary results of the model rely on these death rates, estimates of disease incidence were included for informative reasons. The disease rates for cancer were taken from the well known Seer cancer statistics. Disease rates for cardiovascular and all other diseases were estimated from a variety of sources and probably are less accurate than are those for cancer. But errors in rates of disease will have little effect on the Well Days computations. In addition to the adjustment for smoking, the primary set of death rates used by Life Ahead also is for a population that is assumed to not take diet supplements, and that does not take advantage of a few other smaller risk factors as physical examinations, mammograms, etc. This makes valuation of these options more direct and accurate. Attempts were made to adjust the death rates in the model for these other factors so that overall results of the model should forecast values for year 2000 life expectancy at average population risks for men and women to within about one year from ages 50 through age 95.
The Life Table Method: Cancer and the atherosclerosis that causes most Cardiovascular diseases are biochemical processes that proceed gradually over the decades of a lifetime. (See Atherosclerosis - a Chemical Process and Cancer - a Chemical Process) To reflect this properly, Life Ahead as a Life Cycle Model computes an incidence of each death and disease year by year, a population survival at year, and constructs a new life table to life expectancy for every combination of or change in health risk factors. Because the major health risk factors of our population change with age, life tables of the values of major risk factors for the base US population accompany the model. Major risk factor values now included for all population age years and sex are Body Weight, Total Serum Cholesterol, LDL Cholesterol, HDL Cholesterol, Triglycerides, Cardiofitness/exercise, and Systolic and Diastolic Blood Pressures. Values of these factors at age for men and women are mostly based on statistics published by NIH. . Values at population age for Cardiofitness were developed as part of the Life Ahead project. (See information on Cardiofitness). The actual average or base values for populations assumed for these major risk factors are listed on this website by age and sex in some of the Life Ahead analyses by factor in the Research Library.
A risk of each major health factor is taken in reference to these average life table values. For example, the present life table values of total serum cholesterol and weight for a man of age 50 are 213 mg/dl and 171 pounds. These life table values at age all are assigned a risk for each involved disease of 1.00. Any less favorable value of a factor is assigned an appropriately higher risk, any more favorable value is assigned a lower risk of disease. Thus the model starts with the actual life risks of the non-smoking US population and computes differing death rates only in relation to how some new life risks vary from those of the average population. These table values also are default risks. If no values for these major risk factors and other factors are entered into the program, Life Ahead simply computes the lifetime rates of disease by year, life expectancy and Well Days as those of the average US population of non-smokers. As noted above, an approximation is that this average population also is assumed to take no diet supplements or not to use a few health options such as physical exams, mammograms or female hormones.
This method thus provides risks of death and disease that should approximate actual real values. Importantly, Life Ahead recognizes that risks accrue as part of a gradual biochemical progress of disease during life. As example, total serum cholesterol and other cholesterol values determine in part a rate of atherosclerosis that gradually clogs arteries during life. A man having a usual 260 total cholesterol probably will have substantially narrowed coronary arteries by age 50. If cholesterol is then lowered to 200, this narrowing will not change immediately but probably will persist for many future years. Another man having usual cholesterol during life of 200 usually will have only modest artery narrowing at age 50. Conventional risk factors or models assign each of these men the same risk, that of a snapshot at year of a cholesterol of 200. But the man with the narrowed arteries really will have a much higher risk. Life Ahead computes an actual life profile of serum cholesterol during life from the inclusion of as many earlier measurements as possible. It then recognizes a difference in risk via the Artery Blockage Model that computes likely artery narrowing based on cholesterol values at each prior year.
Many factors in Life Ahead are valued by duration of that factor, for differing values of factors at different years of age, and for differing times after a health factor is changed. The risk of smoking accumulates gradually as years of smoking increase, and this risk can persist in part for up to two decades after smoking is stopped. Other factors that can depend importantly on time and duration include use of diet and diet supplements, antioxidants, cardiofitness, mammograms, female hormones, and use of cholesterol drugs. The risk of some factors as cholesterol and smoking also vary substantially with age. These changes in risk also are recognized in Life Ahead via differing age-related risk factors applied at each successive year of life. More on how each factor is valued is provided in the Research Library. Thus a health risk of today depends not just on habits of today, but also may in part depend on habits of the past and the prior age at which habits were changed. A risk in the future will depend not only on a change in habits but on how long the change in habits is maintained. .
A Truly Basic and complete Life Cycle Model should produce results for ALL WORLD POPULATIONS: A fully correct Life Ahead model should be able to reproduce not just the US population death rates of its 1990’s basis, but should be able back-forecast US population death rates for years in the past. It should be capable of forecasting rates of death and disease into the future and beyond the dates of base NIH rates used in its development from differences in health factor levels that then exist. The program also should be able to explain the widely differing death rates of disease in the various countries of the world and how these vary over the years. It is unlikely that the present model will have this important capability yet, but any verified failure of the model to do this on the US population will identify a defect that should be remedied. For a differing country population, the model might identify a true difference in genetic risk. But with this valued, the program should be able to forecast present and past death and disease rates for another world population.
A brief review suggests that the present model will roughly back-forecast most of the large increase in coronary heart disease of the US population from 1900 to 1960 as due to changes in population smoking, serum cholesterol, and cardiofitness from physical activity. The subsequent decline in risk since 1960 is due mostly to reductions in serum cholesterol and smoking. The diet model also should be able to and probably does explain long puzzling facts as example for the much lower rates of coronary disease obtained from the so-called Mediterranean and other diets. Hopefully, others will undertake to learn if the present model can accomplish this, and if not, advise what factors in the model need improvement.
About Race and Origin: Standard vital statistics report rates of disease and death by race, as for example White, Black, Non-White, Asians, etc. Life Ahead now uses total population values and includes no segregation of results by race. A problem here is that differing races can have quite differing life style habits, major health factor profiles, and other listed and valued health factors in addition to what may be differing genetic risks. Thus use of raw vital statistics by race would be invalid in a general population model such as Life Ahead. A detailed analysis of average population risk profiles for each the above noted eight major risk factors and a detailed comparison of actual average diets and regular exercise and other factors will be needed to determine how much of the difference now ascribed to race is due to the differences in known basic risks and life style habits and how much is due to differences if any in actual genetics. Such information is not now available here.
It is well established that as various world populations move to the US and adopt US style lifestyles their previously differing health risks move toward those of the US. The Life Ahead technology provides what may be a useful and more robust basis for identifying true differences in the genetic risks of populations by its method for adjusting for effects of multiple differences in identified risk factors, diet, exercise, other life style factors. Yet it seems likely that even if some true genetic health risks of different races exist, the effect of changes in diet and exercise and other lifestyle habits on health and longevity will remain similar for those of differing races. Thus Life Ahead probably will provide useful health guides for people of all races.
The Life Ahead Inputs: Life Ahead first asks for sex, age, height, weight, and for up to 120 additional factors that might affect present and future health. Most values can be entered easily into eight or nine entry screens, and need entry only once. Information can be added or edited any time, but some information that should be gathered in advance includes recent and any past measurements of cholesterol factors (Total, and if available LDL, HDL, Triglycerides), recent Blood Pressures, the bottles of any Diet Supplements used so that amounts from their labels can be entered. A diet entry is optional, and the program will compute results with or without a diet entry. But results about diet can be so interesting that everyone should complete one. A cardiofitness test will be very useful if facilities for this test are available. A first diet entry should be as accurate as possible and represent a most usual recent weekly diet. The Demo program includes as weekly options No 1 a roughly average US diet; No 2 a quite good diet, and No 3 an unhealthful diet. A comparison of a users diet results in Well-Days with results from these demo options with each including the same dietary supplements will give some idea of how the user diet compares with these good, average, and poor health diets. And Life Ahead will identify explicitly how each diet entered can be improved to produce lowest risk of major diseases..
The previous section “What Life Ahead Computes” describes more about this.