No matter how far fruits or vegetables travel, whether they’re grown organically or conventionally, they’re packed with vitamins, minerals and other necessary nutrients. The men and women in the fields try to grow foods with an eye to boosting the health factor, but researchers say it’s hard to measure the precise impact.

Consider the orange, a fruit high in vitamin C, which boosts the body’s immune system. One from a tree in Florida and another of the same variety grown in California won’t have identical values of the scurvy-fighting vitamin.

“There's going to be slight differences in the amount of vitamin C by the cultivar, the type of fruit that it is, where it's grown, how long it's been on the store shelves,” Iowa State University food science and human nutrition professor Ruth MacDonald says.

As important as farming practices can be, MacDonald says they’re not the most efficient way to increase a food’s healthfulness. That is best done in a lab or at a processing center, where iron is added back into flour and milk is fortified with vitamin D.

“It's easier to add the nutrients to the food after the fact,” she says, “and it's more consistent and it's more bioavailable.”

Read the full article about measuring farmers' influence on food nutrition by Amy Mayer at Harvest Public Media.