Millions of people around the world could face threats to their health because of changing environmental conditions caused by human activity, according to two new studies from Harvard T.H. Chan School of Public Health. Due to variations in environmental conditions, significant alterations are highly likely to be caused in quality of key crops.

One study found that growth of nutrient-rich crops could face severe decline because of decreasing numbers of food pollinators such as bees. These crops play a crucial role in keeping diseases at bay among human beings.

Researchers say that pesticide use and destruction of habitats are to be blamed for dwindling numbers of pollinators. Findings of a second study have showed that foods could lack enough zinc levels due to increasing levels of atmospheric carbon dioxide (CO2), which could greatly expand zinc deficiency.

Details of the study on pollinators will be reported in The Lancet and the study about zinc will appear in Lancet Global Health.

Biophysical conditions were very stable when all of human civilization took place, but human activities are now altering those conditions at an unprecedented rate, said Samuel Myers, senior research scientist in the Harvard Chan School’s Department of Environmental Health, who is senior author of the pollinator study and lead author of the zinc study

“Whether we’re talking about land use, deforestation, degradation of global fisheries, disruption of the climate system, biodiversity loss, appropriation of fresh water, changes to aquatic systems—all of the changes are profound and they’re accelerating, and they represent a significant challenge to global health”, said Myers.