July 26: Average adult heights in many countries appear to have peaked 30 to 40 years ago and have declined slightly since then, according to a new study that the authors say is based on the largest set of such data ever gathered.

They combined results from 1,472 studies in 200 countries looking at the measured - rather than self-reported or estimated - heights of about 18.6 million people born from 1896 to 1996. The study was published in eLife.

Dutchmen born before 2000 were the world's tallest, and Guatemalan women born before 1900 were the shortest, the study found. South Korean women and Iranian men had the greatest gains in height over the last century. But Guatemalan women also grew, rising from 4 feet 7 inches to 4 feet 11 inches, on average.

Latvian women are now the world's tallest.

Height is strongly influenced by the mother's nourishment during pregnancy, and the child's during infancy. Height is also linked to overall health and well-being. Taller people tend on average to live longer and to have fewer cardiac and respiratory problems. Some studies have shown that they are paid higher salaries.

American men reached their maximum average height in 1996, and women in 1988. Two of the study's authors, James Bentham and Majid Ezzati, both of Imperial College, London, speculated that the decline could be because of worsening nutrition standards for poor Americans.

NEW YORK TIMES NEWS SERVICE