My 18-year-old daughter has recently decided to reduce dairy in her diet, which includes switching from drinking cow’s milk to drinking almond milk. She has done this because she says that drinking cow’s milk causes bloating, and she may be right. Cow’s milk is rich in lactose and if you lack the enzyme lactase — which many people do — your body will find the lactose difficult to break down and absorb. Instead the bacteria in your gut will feast on the lactose, producing gas and gut irritation. My daughter decided to see if she is genuinely lactose intolerant by taking dairy out of her diet, then reintroducing it gradually. It appears that she is.
So I am supportive of her decision. What worries me, however, it that she is part of an accelerating trend away from dairy, particularly among young women, that could have serious health consequences for the next generation.
There are lots of nutrients that cow’s milk has in abundance that other milks, derived from soya, almonds or oats, don’t. These include calcium, for strong bones, and something that many people rarely consider: iodine. Cow’s milk is the greatest source of iodine in the British diet and a move away from drinking it is likely to worsen the already high rates of iodine deficiency in the UK.
In the bad old days, before we knew anything about vitamins and micronutrients, iodine deficiency was common and devastating, leading to goitres and cretinism. So it is disturbing that after a century of medical progress it’s back. The UK ranks in the top ten most iodine-deficient nations in the world, which is particularly worrying because iodine deficiency is especially common in young British women.
In 2011 a study measured the amount of iodine in urine samples collected from 737 teenage girls from all over the UK. It found that nearly 70 per cent had levels below 100 micrograms per litre — the acceptable minimum level defined by the World Health Organisation (WHO). Furthermore, 18 per cent of the samples showed very low iodine levels — below 50mcg/l.
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This matters because the effects of being iodine-deficient can be profound and long-lasting. Iodine is essential for the production of thyroxine, a hormone that controls all the metabolic processes that go on in your body and, in particular, your metabolic rate. Having low levels of iodine leads to low levels of thyroxine, which in turn leads to a lower metabolic rate, weight gain and mood swings. In other words, a lack of iodine in your diet can make you fat (I feel a potential marketing campaign coming on). More worryingly, even mild iodine deficiency in a pregnant woman can have a significant impact on the brain of her developing foetus.
A long-running study in the West Country, called the Avon Longitudinal Study of Parents and Children, has followed a large group of women going through pregnancy and beyond. It found that most of them were iodine-deficient. It also found a strong link between the women being mildly or moderately deficient prenatally and their children’s reading ability and IQ score when they were tested at the age of nine.
Other studies carried out by the WHO have found an IQ difference of up to 13 points between communities that have adequate amounts of iodine in their diet and those that don’t. The WHO’s response to this global problem has been to encourage the addition of iodine to salt, a campaign that has been remarkably successful elsewhere. It is not, however, likely to happen in the UK any time soon, for reasons that elude me.
In the recent past that didn’t matter so much because we were drinking cow’s milk, which is rich in iodine. It matters now that so many people are switching to alternatives. A study carried out by the University of Surrey looked at the iodine content of 47 “healthy” milks (including soya, coconut, almond, rice and oat milk) and found that they had levels of iodine that were 2 per cent of those in cow’s milk.
When it comes to iodine it doesn’t matter if you choose skimmed, semi-skimmed or full fat, they all have roughly the same amounts. It does matter, however, if you go for organic. Another study, published in the journal Food Chemistry, found that milk labelled “organic” has 30 per cent less iodine than conventional milk. The authors suggest that switching to organic milk may increase the risk of iodine deficiency, particularly in “at risk” groups such as pregnant women.
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So what do you do if you want to get enough iodine in your diet, but are lactose intolerant, vegan, or just don’t like cow’s milk? Other foods that are relatively rich in iodine and which are recommended by the experts I’ve spoken to include white fish and seaweed, but are they really as good?
On my BBC series Trust Me, I’m a Doctor we like to test these things out. So with the help of Dr Emilie Combet from Glasgow University we recruited 12 volunteers to compare the effects on their iodine levels of eating white fish and seaweed against milk. On three separate test days our volunteers ate a carefully measured portion of one of these foods. Then, because iodine absorption is best measured by looking at urine, our volunteers had the delightful task of collecting all the urine they produced over the next 36 hours. “Carrying 20 kilos of your own pee up a hill is harder than I thought it would be,” one of them grumbled. No one said science was easy.
After 12 days and countless bottles of urine the results were in. So what happened? After measuring iodine compounds in their urine Combet concluded that our volunteers’ bodies had managed to successfully extract most of the iodine from the milk and the fish. When they ate seaweed, however, things were different. Although the seaweed we gave them contained a similar amount of iodine to the fish and milk, their bodies absorbed only about half as much.
I asked Combet why she thought the seaweed had scored relatively poorly. She said: “We think it’s because the iodine is bound into what is a very fibrous food and that is why our body struggles to break it down.”
So our main finding was that, although seaweed is a good source of iodine, its bioavailability — the amount your body takes in — isn’t that predictable. If you are relying on seaweed as your main source of iodine (if you are a vegan, for example), you will also have to be careful about the sort of seaweed you are eating because the levels vary hugely.
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Pregnant and lactating women need extra iodine, but seaweed is not recommended because of the risk of overdose. You would be better off taking a multivitamin containing iodine, but this is not official NHS policy. It is all rather confusing.
My daughter isn’t a big fan of seaweed — it is an acquired taste — and cow’s milk is still off her menu. Fortunately she likes fish. Personally I am going to stick to drinking the white stuff.
How to test if you are lactose intolerant
When we’re very young we get lots of lactose in our diet, from breast milk or cow’s milk. If, like 75 per cent of the world’s population, you lose the enzyme lactase as you grow older, then any lactose you eat will hang around in your digestive system, where it will be fermented by bacteria, leading to the production of lots of gas. If you are genuinely lactose intolerant, an hour or so after drinking milk you are likely to experience flatulence, diarrhoea, a bloated stomach, cramps and stomach rumbling.
The easiest way to find out if you are lactose intolerant is through an exclusion diet. You remove all lactose-rich foods from your diet for at least a month and see if your symptoms improve. Then gradually reintroduce lactose and see if they recur. If that sounds too low-tech, there are other more expensive tests, including a hydrogen breath test and a stool acidity test.
For the breath test you fast overnight, then swallow a fixed amount of lactose. Your breath is analysed over the next couple of hours. If your body fails to break down lactose, your gut bacteria will feed on it and start producing hydrogen. The downside of this test is that it can produce severe diarrhoea. Instead you may prefer the stool acidity test, which is as straightforward as it sounds. You provide stool samples and if your stools are acidic, that suggests you are intolerant.
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If you are neither lactose intolerant nor a vegan, there is a considerable downside to avoiding dairy products. Cow’s milk is incredibly nutritious (it has to be to feed a growing calf). It’s rich not only in iodine, but also in calcium, vitamin D, vitamin B12, potassium and phosphorus.
Trust Me, I’m a Doctor is on BBC Two on Wednesday at 8.30pm
Iodine: do you get enough?
(According to the NHS, adults require 140 micrograms of iodine a day)
Food/Portion/Iodine
Dairy
Cow’s milk, 200ml, 50-100mcg
Yoghurt, 150g, 50-100mcg
Cheese, 40g, 15mcg
Fish and shellfish
Haddock, 120g, 390mcg
Cod, 120g, 230mcg
Salmon, 100g, 14mcg
Prawns, 60g, 6mcg
Seaweed
Kelp, 1 tbsp, 2,000mcg
Arame, 1 tbsp, 730mcg
Wakame, 1 tbsp, 80mcg
Non-dairy
Egg, 1 egg, 25mcg
Meat/poultry, 100g, 10mcg
Nuts, 25g, 5mcg
Cranberries, 25g, 100mcg
Sources: The Association of UK Dieticians, bda.uk.com; globalhealingcenter.com