Helping children build healthy bones

The CSIRO has recently released a Wellbeing Plan For Healthy Kids with the aim that every primary school aged child will bring home information and a fridge magnet to teach their family how to eat and live well. While this is a wonderful initiative – looking at creating lifelong healthy habits like drinking lots of water, eating breakfast every day, upping the vegetable intake and being more active – the advice on creating strong bones tells a very limited and heavily biased story. Today’s Health Trip looks at the bigger picture about creating a lifetime of healthy bones.

Evidence shows that calcium alone does not create healthy bones

While calcium is the major building block in bone formation, it is totally useless without Vitamin D. This vitamin basically promotes calcium absorption (from the blood) and regulates bone formation and loss. Focusing all our education about bone health on dietary calcium is immaterial is we can’t actually use it.

Vitamin D can be made by the body under the right conditions. It begins in the skin when exposed to UV. Some fatty fish (eg: sardines, tuna, mackeral, eel), egg yolks (though some commercial farming practices can alter this) and cod liver oil also give us Vitamin D. In such a sun drenched land like Australia you may be surprised to learn that a significant number of Aussies are deficient in Vitamin D. Though smog and dark skin can be a factor, the greatest reason for this is the successful education campaign around skin cancer prevention. While we are deligently covering up, slathering on the sun block and avoiding overt sun exposure we are decreasing our chance of developing a deadly melanoma but unfortunately becoming D-deficient and osteoporotic as a side effect. The link above gives some good recommendations on sun exposure for different cities in Australia and New Zealand as well as a good guide to supplementation for all ages.

A report in the EMJA published last year described vitamin D deficiency in Australian children as now being “a significant paediatric health issue”. Another recent study (looking at the higher incidence of Vitamin D deficiency in children with Type 1 diabetes) found that Vitamin D levels in blood samples of Queensland children and adolescents were lower overall than those found in the subjects of the Swedish study.

But don't forget, all the Vitamin D and calcium in the world won’t stop bone loss without adequate weight bearing exercise. Kids who become couch potatoes can’t grow healthy bones.

Other important nutrients for healthy bones

Aside from the Vitamin D issues, there is no debate around the need for adequate calcium intake for many aspects of good health. The debate centres around how much calcium we actually need, the most effective dietary sources and how other foods and substances impact on our calcium bioavailability. Here are some of the major players that are often overlooked in all the ‘official’ hype about calcium:

Sodium: The more salt in your diet the more calcium we pee out. While it is one thing to not have the salt shaker on the table at meal times don’t underestimate the amount of sodium added to processed foods (even some healthy looking breakfast cereals, let alone chips) and restaurant as well as takeaway foods. Raising children to not have a salt craving palate is a great addition to their healthy bone plan.

Phosphorous: This is another mineral essential to the calcium regulation and healthy bone story. Like sodium, this is a case of too much (and rarely, too little) upsetting the calcium applecart. Excess phosphorous gets into the diet from soft drinks, phosphate additives and in diets high in dairy, poultry and meat. We need equal amounts of phosphorous to calcium in our diet in order to use the calcium. The average diet has 2-4 x more phosphorous than calcium!

Magnesium: We need 1/2 as much magnesium to calcium, for the calcium to be used in our body for building strong bones. There are 2 major issues that contribute to magnesium deficiency becoming increasingly common. Firstly the best sources of magnesium tend to come from whole foods like unrefined grains and nuts. But most people eat refined plant foods such as flour and white rice which promotes magnesium deficiency. The other problem is excess calcium. While a cup of whole milk may contain 115 mg of calcium the magnesium content is around 10-15 mg. [Source: Tricky, R. "Women, Hormones and the Menstrual Cycle"]. The average calcium:magnesium ratio in dairy foods ranges from 8:1-12:1 versus the bio availability requirement of 2:1.

Vitamin K: This little talked about vitamin, rich in green, leafy vegetables is another important co-factor in the regulation of calcium in the body. Most Australian children do not get the recommended amount of fruit and vegetables in their diet, so we are likely to learn more about Vitamin K if this trend continues.

Protein: The more protein you eat, especially from animal sources such as meat, poultry and dairy, the more calcium you loose through your urine. For every gram of protein you eat, you loose 1 milligram of calcium. Most official dietary plans do not take this into account. While vegetarian, especially vegan, diets are criticized for an overall lower intake of calcium, it doesn’t take into account that a low animal protein diet causes less calcium loss. New evidence is emerging to show that a balanced vegan requires lower RDI of calcium

Phytates and oxylates: Plant foods however, can reduce calcium utilization. High fibre such as straight bran can reduce calcium absorption. If you had a bowl of 100% wheat bran, you would only be able to absorb half the amount of calcium from other foods eaten at that meal. However, it is rare for someone to eat just bran. Likewise oxylates in some foods such as spinach and beans can reduce calcium absorption. Soaking beans and cooking in fresh water reduces the oxylate content.

Caffeine and smoking (which may include passive smoking) also disrupt the healthy bone story but we would hope kids are exposed to neither of these. Never give your children or teens cola or energy drinks, as the combination of phosphorous and caffeine is a surefire recipe for osteoporosis.

Calcium

While calcium is considered an important building block for healthy bones, the literature repeatedly demonstrates that calcium alone does not build stronger bones in children. Nor does having your RDI of calcium in the form of dairy prevent bone fractures in adults.

Dairy foods are repeatedly promoted as the “best” sources of calcium. Other than supplements, it is true that gram for gram (perhaps with the exception of unhulled sesame seeds and kelp) dairy products contain more calcium than any other food. However, whether these are the best foods to grow healthy bones is debatable considering the issues of phosphorous, magnesium and protein, as discussed above.

Another factor to consider is dairy intolerances and allergies, either to lactose (which is even higher in low fat dairy foods) or the dairy protein. Some indications that your baby or child is negatively reacting to dairy products may include: skin rashes, digestive upsets (like wind, colic, diarhhoea or constipation), mood changes and atopic allergies (such as asthma, eczema or hayfever). Naturopathically we tend to find children who have recurrent ear, nose and throat issues potentially have a higher rate of dairy intolerance.

If your child does have an inflammatory bowel condition, whether caused by a food allergy or common conditions such as Crohns disease, very little of their food sources of calcium may be utilized when loose bowels are involved.

The official rate of dairy allergies in Australia is 1:50 children, however this only includes children who have had immunological testing (not every child with a food allergy is referred for testing) and doesn't include dairy intolerance, meaning the actual occurrence of children not tolerating all or some dairy foods is much higher. Certain ethnicity's, such as children with an Asian background, have a very high risk of dairy allergy and I would advise them to avoid dairy completely. Interesting to note is that approximately 1:4 children with a dairy allergy will also be allergic to soy foods.

How much calcium do we need?

According to the Victorian government the RDI’s for children and teens are as follows:
Babies – 0 to 6 months (breastfed) recommended dietary intake (RDI) 300mg
Babies – 0 to 6 months (formula-fed) RDI 500mg
Babies – 7 to 12 months RDI 550mg
Children – 1 to 3 years RDI 700mg
Children – 4 to 7 years RDI 800mg
Children – 8 to 11 years (girls) RDI 900mg, (boys) RDI 800mg
Children and teenagers – 12 to 15 years (girls) RDI 1000mg, (boys) RDI 1200mg
Teenagers – 16 to 18 years (girls) RDI 800mg, (boys) RDI 1000mg.

The UK Vegan Society has some good resources on non-animal sources of calcium.

Keep in mind these figures assume that there are adequate amounts of co-nutrients and no other factors interfering with the bio availability. Compulsory reading for anyone interested in the whole debate is this excellent article from the Harvard School of Public Health “Calcium and Milk: What’s Best For Your Bones”. Their conclusions are drawn from long term studies (minimum 12 years) of over 100,000 men and women, which makes them the most credible source currently available on the subject. While they question conventional assumptions as to the the amount of calcium required (they suspect it is actually lower than the official recommendations) on the issue of dairy for strong bones they conclude:

Currently, there's no good evidence that consuming more than one serving of milk per day in addition to a reasonable diet (which typically provides about 300 milligrams of calcium per day from nondairy sources) will reduce fracture risk. Because of unresolved concerns about the risk of ovarian and prostate cancer, it may be prudent to avoid higher intakes of dairy products.*

What else can stop a child growing healthy bones?

As if the average Aussie diet, lack of UV and not doing adequate amounts of weight bearing exercise wasn’t enough to complicate the healthy bone picture, the use of steroids (such as cortisone used in asthma and eczema) and the increase rate of eating disorders from a young age also has a detrimental impact on the development of healthy bones.


So you can see, healthy bones is not all about having 3 cups of milk a day after all.



* (My emphasis). Along with the concerns that the Harvard studies mentioned around dairy intake and an increase in ovarian and prostate cancers, other studies show a link between drinking milk and developing Type 1 diabetes and the issue of Low fat dairy foods and infertility