Disability-adjusted life years or DALYs are a universal measurement that researchers and policymakers use to calculate how diseases and medical conditions affect the length and quality of life for a given population.
Basically, one DALY equals one year of full, healthy life that you may lose because you're sick and have a high risk for certain conditions, disabilities, or due to death. The number of years may add up based on how severe your illness might be.
The DALY is used to understand and evaluate the “burden of disease” in different populations. This means experts look at the health, socioeconomic, political, environmental, and economic factors that affect overall health outcomes.
DALYs were first used in the early 1990s. Experts also use it to compare how certain conditions affect the total number of years lost across different populations locally, regionally, and globally.
How Is DALY Calculated?
To calculate DALYs, experts use two other health metrics:
- Mortality or years of life lost (YLLs)
- Morbidity or years lived with disability (YLDs)
YLLs refers to the number of years of life lost due to premature death. YLDs refer to the causes and number of healthy years one might lose from their life due to disability and sickness.
DALY is calculated as the sum of YLLs and YLDs due to health conditions or diseases that affect a particular population. The DALY scale is between 0-1. 0 implies perfect health while 1 equals death.
For example, if you take a look at a set of people who are 15 years old, you might assume that they'll live to close to 80 if they don't develop severe health conditions like diabetes, asthma, a road injury, or cancer. However, if one of them dies at age 15 due to a car accident, you can calculate DALY as 80 minus 15 YLL (years of life lost due to death). In this case, you can skip YDL as there's no health condition or disability involved.
80 minus 15 would equal 65 DALY – each point for a year of healthy life lost.
You can add back DALYs, or full years of healthy, productive life, to the overall score if you get treatment, make lifestyle changes, or get medical procedures to improve your health outcome.
What Medical Conditions and Disabilities Can Affect DALY?
DALY takes into account a wide range of health conditions, injuries, and disabilities that affect a given population to calculate a score between 0 and 1.
This can include:
- Communicable diseases such as HIV, measles, COVID-19, or bacterial or viral infections that cause gut problems.
- Tuberculosis, meningitis, and tetanus (often seen in low-income countries)
- Lifestyle-related health conditions like diabetes, heart disease, cancer, and high levels of cholesterol
- Birth defects
- Aging and gene-related conditions like Alzheimer's
- Pregnancy and pregnancy-related conditions
- Nutritional deficiencies
- Physical disabilities like blindness or deafness
- Physical violence or injuries caused by road accidents
- Substance abuse
- Mental health conditions like anxiety or depression
- Back or neck pain
DALY vs QALY
Like DALY, quality-adjusted life year (or QALY) is another popular metric that experts use to measure the length and quality of life of an individual. It's basically 1 year of life you live when you're in perfect health. This metric is mostly used in high-income countries in the West.
The difference in approach between the two metrics is that while DALY is often used to measure the number of years lost due to sickness or death, QALY is used to measure the number of years you might gain when your quality of life improves.
How Can You Improve Your DALY Score?
Research shows you can improve the total number of years lived in full health and lower the burden of disease if you:
- Lower your body mass index (BMI). It's a scale used to measure a person's body fat using their height and weight.
- Cut back or quit smoking.
- Cut back or quit alcohol.
- Improve physical activity and exercise.
- Eat balanced, nutritious meals with fruits and veggies. Preferably stick to a Mediterranean diet.
One study that looked at over 33,000 men and women found that if you make and stick to all of the lifestyle changes toward a healthier life, it can improve your DALY score.
Not only will it boost your overall health outcome but also add a minimum of 2 years of full health to your life compared to those who don't make any lifestyle changes.
Why Are DALYs Useful?
DALYs allow experts and policymakers to take a large-scale look at what level of burden a particular disease might have on a given population and make recommendations to improve accordingly.
Studying the burden of disease can help understand:
- Main causes of death by age, sex, and disease
- Causes of death in different parts of the world
- Numbers of people with various diseases and disabilities based on geography
- Number of people who become ill each year locally and globally
- What causes certain populations to lose good health and live a full, productive life
For example, if you take a look at young people between ages 10-24, they have many more years of healthy life to live, and usually, death or severe illness is rare among this population.
DALY scores can allow researchers to look at the impact of certain conditions such as growing cases of diabetes or heart disease, or physical disabilities, and see how it can affect their ability to live a long, healthy life.
This information can be used to improve health services, make recommendations for healthier lifestyles to live longer lives, and guidelines for particular age groups.
Are There Any Limitations to DALY?
DALY uses only a single number to account for all the costs and losses caused by diseases or disabilities, but it might not take the full picture into account. That's because not all diseases or disabilities are equal nor is your ability to manage them.
For instance, having asthma for a few years is not the same as living with schizophrenia. So it's complicated to calculate without taking into account the social factors that affect different international populations' health outcomes.
For example, disabilities such as injuries, illnesses, and developmental problems such as speech or hearing don't necessarily mean that you cannot live a full, healthy life.
In fact, your overall quality of life might vary significantly depending on where you live and whether you have access to quality health care, social support, accommodations in your immediate environments to help you with your daily activities, and your ability to get timely medical treatment or rehabilitation you might need.