Patty Sullivan is stumped by the dairy case. One kind of milk promises to make her children smarter. Another claims to come from healthier cows. Unable to sort all that out, she reaches for conventional Costco milk.

"I find it very confusing," said Sullivan, of Catonsville, Md., who picks up five gallons a week for the preschool she runs. "You need a research degree to find out the differences. And is it really that much better for you?"

Not long ago, consumers had to ponder only one thing before hefting a gallon jug into the shopping cart: How much fat did they want? Then, more than a decade ago, organic started showing up in traditional supermarkets.

Contradicting research

Today, the world of milk is even more rarefied - and more confusing, because the milk trucks are moving more quickly than the science. Researchers can't even agree if milk "does a body good," much less which kind is best. While consumers can have their pick of more milk varieties than ever before, they also have more questions about a product considered to be a cornerstone of childhood nutrition - one that each American, on average, consumes at a rate of 24 gallons a year.

There's milk from grass-fed cows, said to be more nutritious and better for the environment. Milk with added omega-3 fatty acids, touted as boosting brain function. Nonhomogenized milk that fans are willing to shake before drinking - in glass bottles, no less - on the premise that their bodies won't absorb as much fat if it hasn't been blasted into tiny bits.

Ultra-pasteurized. Low-pasteurized. Unpasteurized "raw" milk. With soy, rice and almond milks suddenly mainstream fare, the dairy case has become more crowded than a feedlot. And none of it is cheap.

While Sullivan spent about $2.25 a gallon for milk at Costco, Wendy Johnson, a special-education teacher, pays more than twice as much for organic. She shells out even more - about $14 a gallon - for individual, juice box-like containers of organic milk for when the family's on the go.

Johnson figures organic is best for her 5-year-old daughter, but she has some doubts, precisely because of those handy "shelf-stable" boxes that don't need refrigeration.

"If you can put it on the shelf, what's left in it?" Johnson wonders.

Is it good or bad for you?

Not that Johnson can take it as a given that milk is good for her daughter in the first place.

Just last month in the American Journal of Clinical Nutrition, Purdue University foods and nutrition professor Connie Weaver wrote that milk is an important source of calcium and other nutrients, improves bone health and reduces the risk of stroke and some cancers. Research has put to rest concerns that it might increase prostate cancer, she noted. But in the same issue, University of North Carolina nutrition scientist Amy Joy Lanou argued that milk increases prostate and ovarian cancers. Her advice: Stay away from the stuff.

Even the experts who think milk is healthful don't agree on much else.

The National Dairy Council and other industry groups contend that all milks are created equal. The U.S. Food and Drug Administration agrees, finding "no significant difference" between organic milk and what flows from cows given synthetic growth hormones to boost production.

"We wouldn't favor one type of milk over another," said Michael Herndon, an FDA spokesman. Like the Dairy Council, Herndon dismissed the various milk varieties as pure "marketing."

But food-safety and sustainable-farming advocates maintain that organic milk is safer. Even if the synthetic hormones, approved by the FDA in 1994, do not show up in conventional milk, they say, they seem to raise the level of other, naturally occurring hormones in the milk that could pose problems for humans. They also contend that artificial hormones are rough on the cows, causing more infections that, in turn, lead to more antibiotic use on the farm.

Many unknowns

In any case, these advocates say, there are too many unknowns.

"I think there's a real void in the science," said Patty Lovera, assistant director of Food and Water Watch, a consumer group based in Washington. "That just wasn't where the (agricultural research) focus was. It was how to be bigger, how to get faster."

There is one point of consensus: Cows that feed on grass produce milk that's higher in omega-3 fatty acids, vitamin E, beta-carotene and an antioxidant called conjugated linoleic acid - all good stuff for the body.

To make milk worthy of the U.S. Department of Agriculture organic label, cows cannot be treated with antibiotics or synthetic growth hormones. The animals must be given feed produced without chemical fertilizers and pesticides. And the cows must have "access to pasture."

The pasture part is problematic because the government has not spelled out what "access to pasture" means. As for milk marketed as "grass-fed," the FDA has not defined the term at all.

On this point alone, Big Dairy and food activists find common ground.

"Grazing is the key," wrote Rusty Bishop, director of the Center for Dairy Research at the University of Wisconsin in Madison. "The problem is that the majority of organic fluid milk on the market is from cows on pasture an average of 60 partial days, and pasture grasses make up less than 5 percent of their dryweight feed intake."

Bishop's research center bills itself as independent but receives substantial funding from the milk industry. His comments about grazing are part of a June 2007 study that otherwise pooh-poohs the purported advantages of organic milk.

But his grazing gripe could have come out of the mouth of John Peck, who hails from the other side of the milk debate. The executive director of the Madison, Wis.-based Family Farm Defenders worries about factory farms co-opting the organic label and wants the government to establish grazing standards.

So while he agrees with Bishop on grazing, Peck's milk mantra couldn't be more different. "The best milk is milk that's unhomogenized, unpasteurized, grass-fed, in a glass bottle, from a farm within 20, 30 miles of you," Peck said.

Pros and cons

That sort of certainty is harder to come by in the supermarket aisles, even for consumers up on the latest nutrition news.

Greg Resch, general manager of David's Natural Market in Columbia, Md., buys Horizon Organic Milk Plus DHA Omega-3 Whole Milk Ultra Pasteurized for his family. The milk costs $4.99 for a half-gallon at David's, a small store that devotes an entire four-door refrigerated case to milk.

Resch chooses that particular milk because it is supplemented with docosahexaenoic acid or DHA, an omega-3 fatty acid that's derived from algae and thought to promote brain development. His kids aren't big on fish, another source of the nutrient, so the milk is his way of slipping a little brain food into their diet.

Resch isn't thrilled that the milk is ultra-pasteurized, heated to a temperature higher than what's necessary for normal pasteurization. That's done to extend the shelf life for many brands of organic milk, which tend to sit longer because they're pricey.

Resch knows there are pros and cons to each choice.

"It can get almost crazy sometimes," he said. "You can only do so much to Mother Nature."