The relationship between dog size and life expectancy has not been fully elucidated, but scientists believe that large dogs die young due to their rapid growth, but also the way people breed them.
Take the one-year-old Great Dane. From birth to the first birthday, this breed increases 100 times in weight, while e.g. the weight of a wolf increases 60 times, a poodle 20 times, and a human only three times. Due to the sudden and rapid growth, various physical problems can occur, especially the improper development of the bones, hips, and spine.
Another theory is that larger races age faster. Giant races are more prone to health problems as well as developmental disabilities. They have a more frequent occurrence of muscle and gastrointestinal diseases, as well as tumors. In addition to the problem of rapid growth, there are side effects of selective breeding of dogs to achieve the largest possible breed.
The absolute champions of longevity are Chihuahuas (18-20 years), Beagle (15+ years), Maltese (15+ years), Pekingese (15 years), Poodle (15 years), Dachshund (14 years)… Unfortunately the shortest lifespan of only 5 to 8 years old: Great Dane, Great Dane, Bernese Mountain Dog, English Mastiff, etc.