If the advertising of the very early '90s taught us anything, it can be summed up in the following slogan: "Milk: It does a body good." But does it really? Here, we weigh the nutritional pros and cons of milk.

Cow's Milk: The Nutritional Basics

From a nutritional standpoint alone, cow's milk has quite a lot going for it, the New York Times points out in their examination of the topic.

An eight-ounce glass of cow's milk naturally contains about eight grams of protein and almost a third of the recommended Percent Daily Value of calcium. Cow's milk also naturally contains nutrients like potassium and vitamin B12. Cow's milk is also usually fortified with vitamins A and D.

Those statistics are pretty much consistent regardless of the particular fat content of the cow's milk you're drinking, although whole milk is significantly higher in fat and calories than the nonfat version. An eight-ounce glass of whole milk has 150 calories and eight grams of fat, including five grams of saturated; an equivalent glass of nonfat milk comes in at 90 calories, with no fat.

Dairy's Dark Side: The Link Between Milk and Cancer

But of course, nothing is ever so simple. While cow's milk of all stripes (spots?) has some obvious health benefits, and also some less obvious ones (there's very, very tenuous) evidence it can help you lose weight), dairy consumption may come with a dark side.

As the Guardian has pointed out, studies have been suggesting a link between milk and prostate cancer since the 1970s, and Men's Health points to a 2010 Canadian paper which found men who consumed more dairy products had double the risk of prostate cancer than their milk-abstaining peers.

Mother Jones reported on another study by Harvard researcher Ganmaa Davaasambuu, which found that consumption "strongly correlated with the rates of breast, ovarian, and uterine cancers in 40 countries." Davaasambuu suggests that the culprit isn't milk itself, though — it's the hormones that come with it, even in milk that's labeled hormone-free.

When she and her colleagues compared milk from the U.S. and Japan — both countries with higher rates of breast and prostate cancer — to milk from Mongolia, where the rates of those cancers is low, they found that the Japanese and American milks had much, much higher levels of sex hormones. That's because in the U.S. and Japan, dairy cows are milked for 10 months out of the year — which, Mother Jones explains, "is only possible because she is impregnated by artificial insemination while still secreting milk from her previous pregnancy." And milk from pregnant cows — surprise! — has a lot more hormones than milk from non-pregnant ones.

The Bottom Line on Milk

More research is needed before we can draw any definitive conclusions, and doing that research is … complicated. As Mother Jones notes, the NIH denied Davaasambuu funding for a follow-up study, "arguing that the dairy systems and human populations in the two countries were too different to merit comparison." It's worth noting too, as always, that correlation is not causation, and that milk consumption is just one variable in a tangled web of interrelated lifestyle habits.

So what, then, should we do with this information?

A good first step is always to be informed about the milk purchases you're making. As we recently discovered, "organic" doesn't always mean organic, but there are consumer resources that can shed light onto the source of your milk. At whereismymilkfrom.com, you can learn about where their milk came from and the grazing practices of different farms. Cornucopia Institute gives out a dairy scorecard.