Growth is a double-edged sword.
How do hormones in milk affect growth, puberty, and health?
Nutrition Diva is hosted by Monica Reinagel. A transcript is available at Simplecast.
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Hello and welcome to the Nutrition Diva podcast, a show where we take a balanced look at the evidence surrounding common dietary dilemmas so that you can make informed choices about your own diet. I’m your host Monica Reinagel and today’s topic was suggested by Sophie, who wrote:
"What about hormones in milk? My toddlers drink it every day, but my friend said hormones in milk promote growth in height and potentially of tumors also. Plus they are hormonally active, bringing kids into puberty earlier. Is this true? Is organic different? What are the alternatives?"
Cow’s milk (as well as milk from other mammals, like sheep or goats, or even humans) contains various naturally occurring hormones, including one called bovine somatotropin. Dairy cows are sometimes given a synthetic version of this hormone (rBST) to boost milk production. Organic dairy operations do not use rBST. But because all cows produce bovine somatotropin naturally, organic milk contains this hormone as well.
In fact, hormone levels are not significantly higher in milk from rBST-treated cows than from non-treated cows. What’s more, this hormone is not biologically active in humans, so even if it were absorbed from drinking milk, it wouldn't be expected to have any effect on health.
Another concern has to do with the presence of another hormone in milk, called IGF-1. Our bodies produce insulin-like growth factor (or IGF-1), especially when we are kids, when it is critical to proper growth. When we reach adulthood and stop growing (taller, anyway), levels of IGF-1 decline, but not to zero. The hormone continues to play an important role throughout life, helping to preserve bone and muscle tissue, for example.
Growth is a double-edged sword, however. We want to promote the growth of bones and muscles but we certainly don’t want to promote the growth of cancer cells or tumors. There is some epidemiological evidence that shows an association between higher IGF-1 levels in the blood and higher cancer risks in adults. But subsequent studies have failed to confirm these reports or have found weaker relationships.
But with that in mind, let’s consider how drinking milk might affect IGF levels.
Some studies show that adults who drink a lot of milk have slightly higher levels of IGF-1 in their blood than people who drink no milk. However, we see the same effect in people who drink soy milk. In fact, the amount of protein that you take in (whether from dairy, soy, or other sources) has a more direct effect on IGF-1 levels than dairy intake. And, as I mentioned, the link between higher IGF levels and cancer risk is murky, at best.
Some studies have found that breast cancer risk is actually lower in moderate milk consumers than in those who drink no milk. Frankly, in terms of cancer risk factors, milk consumption ranks pretty low on the list, far behind things like excessive body weight or alcohol consumption.
But, back to Sophie’s toddlers: Could drinking milk be related to early puberty?
Kids seems to be going through puberty earlier and earlier, which has a lot of people concerned. One suspected culprit in early puberty is environmental contaminants, such as the forever chemicals we’ve been hearing so much about. Unfortunately, there’s not a whole lot we can do as individuals to avoid exposure to these chemicals.
Of those factors that we actually can control, the two that appear to have the biggest effect on the risk of early puberty in boys are being overweight or obese (which increases the risk) and physical activity (which decreases the risks).
For girls, there have been some observational studies, mainly from Western settings, suggesting that breastfeeding was linked to a slightly later onset of menstruation, whereas higher milk consumption was linked with earlier onset. But these studies didn’t always control for variables such as different socioeconomic conditions. Other better-controlled studies have found that neither breastfeeding nor childhood milk consumption was associated with the age that kids enter puberty.
In terms of growth and development, drinking milk does not appear to pose any substantial risk to kids. In fact, as a source of quality protein and calcium, it appears to play a positive role, especially in bone growth. That said, there are plenty of ways to get protein, calcium, and vitamin D without consuming dairy products. For those who prefer to avoid cow’s milk, you can buy non-dairy alternatives made from soy, rice, almond, oat, coconut, peas, or hemp. Each has its advantages.
Soy and pea milk are the highest in protein, providing between 8 and 11 grams of protein per cup, which is comparable to cow's milk. Legumes, such as soybeans and yellow peas, are also a relatively complete source of protein, although not quite as complete as dairy.
Hemp, flax, and walnut milk are all good sources of omega-3 fats, a nutrient that is often lacking in the Western diet. If your diet does not include fish, this could be a way to fill that gap.
If you’re counting calories, almond milk tends to be quite a bit lower in calories and sugar than most of the other non-dairy milks. It's also fairly low in protein. But don't expect the same benefits you'd get from eating almonds. Virtually all of the fiber and heart-healthy monounsaturated fats that make almonds so healthy have been removed.
Rice milk is one you’re least likely to be allergic to. However, it’s the lowest in protein and tends to be higher in sugar and calories.
Oat milk is another newer entry into the nondairy field. People tend to like its creamy texture, especially in coffee. It's also a more sustainable option than nut- or rice-based milk. Another plus is a small amount of fiber. We’re only taking 1 or 2 grams per serving, but oat fiber has some unique benefits in terms of lowering blood cholesterol and blood sugar levels.
Plain unsweetened coconut milk is very low in calories and carbohydrates, with only about half as many calories as skim milk. However, coconut milk contains no protein and is often described as watery and tasteless.
No non-dairy milk is appropriate for use as baby formula. Once kids are eating table foods, however, any of the non-dairy options would be fine. Obviously, you'll want to avoid ingredients that your child is allergic to, such as soy or nuts. But a soy or pea-based beverage will provide the most protein for growing bodies. A brand that's fortified with calcium and D will help build strong bones.
To recap: there's no concrete evidence that milk hormones pose a threat to kids. And dairy has its nutritional advantages. But it's not irreplaceable, and many alternatives are available.
I know it can be frustrating that nutritional dilemmas like this so often don’t have a clear-cut, definitive answer. So often, the research is inconclusive or contradictory. There are so many factors to weigh and consider—including things like convenience, cost, and preference.
At the end of the day, there’s no diet that guarantees optimal health, because our health is impacted by so many things besides diet. But I hope that an objective look at what is and isn’t known, and the relative impact of the different factors you’re considering, helps you feel more confident about the food choices that you make for yourself and your family.
If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206
I also wanted to mention a special program I am offering with registered dietitian and self-compassion expert Cassie Christopher. It focuses on Body Image Repair and Resilience. We are so excited about this collaboration and this work. If you’d like to hear more about what led us to this topic you can check out our conversation on the Change Academy podcast. And there’s also more information about the program itself at https://weighless.life/body