According to the latest GBD report (2020), which covers 204 countries and territories from 1990 to 2019, the global population had a total of 1.5 billion YLDs in 2019, which means that people spent 1.5 billion years in less than optimal health due to various causes²-***. The leading causes of YLDs in 2019 were low back pain, headache disorders, depressive disorders, musculoskeletal disorders, and anemia². The report also estimates that about **95%** of the world's population had at least one health problem in 2019, while about **40%** had more than five health problems².

However, these numbers should be interpreted with caution, as they are based on assumptions, models, and estimates that may have uncertainties and limitations. Moreover, they do not capture the full complexity and diversity of human health and sickness, as they rely on standardized and aggregated measures that may not reflect the individual and contextual factors that affect people's experiences and perceptions of their own health. Therefore, they should not be taken as absolute or definitive answers, but rather as approximate and indicative values that can help us understand some aspects of sickness in the world.

***
The statement "people spent 1.5 billion years in less than optimal health" is based on the concept of years lived with disability (YLD), which is one of the indicators used by the Global Burden of Disease Study (GBD) to measure the impact of different diseases and injuries on health and well-being.
YLD is calculated by multiplying the number of people who have a certain health condition by the average duration of that condition and by a weight factor that reflects the severity of that condition on a scale from 0 (perfect health) to 1 (equivalent to death). For example, if 10 million people have a condition that lasts for 5 years and has a weight factor of 0.2, then the YLD for that condition is 10 million x 5 x 0.2 = 10 million years.
The GBD report estimates the YLDs for hundreds of different causes of ill health and disability, such as low back pain, headache disorders, depressive disorders, musculoskeletal disorders, and anemia. By adding up the YLDs for all these causes, the report obtains the total YLDs for the global population in a given year. According to the latest report (2020), which covers 204 countries and territories from 1990 to 2019, the global population had a total of **1.5 billion** YLDs in 2019. This means that people spent 1.5 billion years in less than optimal health due to various causes.

(1) Over 95% of the world’s population has health problems, with over a .... https://www.sciencedaily.com/releases/2015/06/150...

(2) Health statistics - World Health Organization (WHO). https://www.who.int/health-statistics.

(3) There are more viruses than stars in the universe. Why do only some .... https://www.nationalgeographic.com/science/articl...

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