A Glass of Milk: Who Should Drink It, Who Should Skip It, and When Is the Best Time?

One ordinary glass of milk can supply more than half of the iodine an adult needs in a whole day. Yet for a large share of adults around the world, that same glass can mean bloating, cramps and an uncomfortable evening. Milk is a small nutritional treasure chest, but it is not for everyone, and timing matters more than most of us think.

When Milk Was the Mystery: Elvira's Story

Cassandra Peterson, the actress known worldwide as Elvira, Mistress of the Dark, has spoken openly about a long-running health puzzle that left her feeling unwell for years. As The Daily Meal reported, doctors eventually traced the problem to lactose intolerance. Her first step was to cut out milk and most dairy entirely. Later she found she could still enjoy acidophilus milk and certain cheeses, products in which the lactose has already been largely broken down.

Her experience shows two things at once. Milk can be the hidden cause of everyday discomfort, and a lactose problem rarely means saying goodbye to dairy forever.

What Is Really in a Glass of Milk?

Fresh cow's milk is rich in minerals and nutrients, and it is especially worth recommending to everyone who is still growing. A 250 ml glass of milk provides a meaningful share of your daily needs for several key nutrients:

• Iodine: According to the USDA, FDA and NIH Database for the Iodine Content of Common Foods, one cup of milk contains roughly 80–90 micrograms of iodine. That is more than half of the 150 micrograms most adults need daily, as listed in the NIH Office of Dietary Supplements Iodine Fact Sheet.


• Calcium: About a quarter of an adult's daily requirement, important for bones and teeth.


• Vitamin B2 (riboflavin) and vitamin B12: Milk is one of the most convenient everyday sources of both. B12 in particular is found almost exclusively in animal foods.


• Tryptophan: An amino acid the body uses to make serotonin and the sleep hormone melatonin.

Of course, milk contains much more than just this. It also offers high-quality protein, vitamin A, potassium and phosphorus. Best of all, a glass of cold semi-skimmed milk has only around 120 calories, while whole milk comes in at roughly 150.

Watching Your Weight? Keep an Eye on the Glass

Even though milk is not especially high in calories, be careful if you are on a diet. Liquid calories are easy to overlook, and a few glasses a day, plus milk in coffee, can add up faster than expected. Flavoured and sweetened milk drinks are a different story altogether. If you are trying to slim down, our article Hello, and Fattening: Foods that Sabotage Your Diet is worth a read.

Who Should Skip Milk?

Milk is not advised for anyone who is sensitive to lactose. Lactose is the natural sugar in milk. To digest it, the body needs an enzyme called lactase, and many people produce less of it as they get older. The U.S. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that undigested lactose travels to the colon, where it can cause bloating, gas, abdominal pain or diarrhoea. Johns Hopkins Medicine also notes that symptoms and tolerance levels vary widely from person to person.

The good news is that lactose sensitivity is usually a spectrum, not an all-or-nothing verdict:

• Lactose-free milk has the same nutrients as regular milk, with the lactose pre-digested by added enzymes. The Finnish dairy company Valio was among the pioneers of fully lactose-free milk. A systematic review in the International Dairy Journal concluded that such products can be an important part of the diet for lactose-intolerant people, helping them avoid nutrient gaps.


• Yogurt and kefir are often better tolerated, because their bacteria break down part of the lactose, as described in a review published in the journal Nutrients.


• Hard, aged cheeses such as Parmesan, Cheddar or Emmental contain only traces of lactose, according to the dietary guidance of North Bristol NHS Trust.


• Raw milk is not a solution. Despite popular social media claims, experts interviewed by AAP FactCheck explain that raw milk contains no meaningful amount of lactase and has the same lactose content as pasteurised milk.

If you choose a plant-based drink instead, check the label. As Hoard's Dairyman reported, many milk alternatives contain only a tiny fraction of the iodine found in cow's milk, so it is worth choosing fortified versions or getting iodine elsewhere.

Timing: When Does a Glass of Milk Sit Best?

Milk may also cause trouble in the evening, especially for people with a sensitive stomach. Some people therefore prefer to avoid it later in the day. A popular piece of advice says that milk is welcome before lunch, but not afterwards. And if you skip lunch altogether (read: you swear by an early dinner), it may be better to pass on milk or to reach for a plant-based alternative.

It is fair to say this is more a matter of personal tolerance than a strict rule. For people who digest lactose well, a warm glass of milk is a traditional bedtime drink. Experience Life magazine explains that dairy combines tryptophan with calcium, which helps the body turn tryptophan into melatonin. If, on the other hand, an evening glass leaves you bloated and restless, a morning glass may simply suit you better. Poor sleep has knock-on effects too, as we described in When you sleep too little, your belly grows.

Pairing matters as well. The U.S. Dairy tips for lactose intolerance point out that drinking milk together with food slows digestion and often improves tolerance. A glass with breakfast may go down easier than one on an empty stomach. For more on what to eat in the morning, see Why is it dangerous to eat these foods for breakfast.

How Much Milk Is Enough?

And one more thing worth knowing: a simple rule of thumb some people use is to halve your body weight in kilograms and divide by 10. The result is a rough number of decilitres of milk per day. If you weigh 60 kilograms, that means no more than about 3 dl of milk a day, preferably in the morning.

Keep in mind that this is a handy guideline, not an official recommendation. National dietary guidelines, such as the Dietary Guidelines for Americans, count milk together with yogurt and cheese as one dairy group. That means the yogurt at breakfast and the cheese on your sandwich also count toward your daily total.

What Readers Tell Us

One of our readers, a woman in her fifties, told us she had blamed her afternoon bloating on stress for years. When she moved her daily glass of milk from the evening to breakfast, and later switched to lactose-free milk, the discomfort largely disappeared, without giving up her beloved milky coffee. Another reader, a father of two teenagers, says milk remains the easiest way to get calcium and protein into his constantly hungry, fast-growing boys.

Experiences like these show why there is no single answer for everyone. The best glass of milk is the one your body is comfortable with.

The Bottom Line

Milk is a treasury of minerals and vitamins, especially iodine, calcium and B vitamins, and it is a particularly valuable food for children and teenagers. People who are sensitive to lactose may do better with lactose-free milk, yogurt, aged cheese or fortified plant-based drinks. Everyone else may simply want to pay attention to how much they drink and the time of day that suits them best.