In Baz Luhrmann's famous Sunscreen Song of the nineties, which dispensed worldly wisdom to the young, there's a couplet: "Get plenty of calcium / Be kind to your knees, you'll miss them when they're gone".
It's one of many good bits of advice in that song, and it's one worth remembering, not only with regard to our knees, but for all of our joints and bones.
It's World Osteoporosis Day on October 20, and it's a good time to think about our bone health, which, like most things, is closely linked to what we eat. As we collectively get older, we're facing more osteoporosis cases than ever before; Osteoporosis New Zealand says one in three women and one five men over 50 will suffer a fragility fracture in their lifetimes.
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Osteoporosis happens when the bones become less dense and more fragile; as we age the delicate balance between old bone breaking down and new bone forming can be lost. Bones with osteoporosis look like very loose honeycomb inside, where healthy bones look smoother and denser.
We accumulate our bone density during our first 20 years or so; after our 20s a continual process of repair is going on, ensuring the old worn-out bone is replaced by fresh new bone. So it's really important for those in their teens, especially girls, to get great bone-boosting nutrition as they build up to that peak bone density.
Hormones come into play, too, especially for women after menopause. As oestrogen drops, so does bone density.
That doesn't mean if we're older, though, that we can't do anything about our bone health. We can maintain our bones as we age with attention to a few things.
The main one we all know about is, like the song says, calcium. Calcium is an important component of bone, and we need enough from food, ideally, to maintain our skeletons. Calcium supplements might seem like an easy way to do this, but Osteoporosis NZ says there are safety concerns related to calcium supplements. We're best to get calcium from foods, if we can.
Dairy is the best source of calcium for many of us. Two dairy serves a day should get us to an adequate level (there's no benefit, they say, from getting super-high amounts). A serve of dairy is a cup of milk, a small milky coffee, a pottle of yoghurt or 40 grams of cheese – about a business-card-sized piece.
If you don't eat dairy, look for high-calcium versions of your alternative milks. Calcium is often added to almond or soy milk, since they don't naturally contain very much calcium on their own (let alone many actual almonds). You can get calcium from other foods too: find small amounts in tofu, legumes, tahini, spinach, broccoli and grainy bread.
Vitamin D is another thing that's important for bone health. We mostly get it from safe sun exposure, but it's also in a few foods, including oily fish, milk, eggs and liver.
Magnesium is a mineral that's found in our bones, and is useful for maintaining bone health. Go for nuts, seeds, legumes, dark leafy greens and whole grains.
And it's worth thinking about our sodium intake from salt; high sodium intake is thought to speed up the excretion of calcium in our urine. On the other hand, potassium helps us hold on to calcium – another good reason to eat plenty of plants.
Thirty per cent of our zinc is found in our bones, and there's growing evidence that intake of vitamin K2 is important too. Both of these are abundant in meat, seafood and eggs, as well as legumes, nuts and seeds.
Once we have all that sorted – in other words, we're eating a sensible, whole-food diet – we just need to remember to move. Exercise that puts pressure on the bones – what you'll hear described as weight-bearing exercise – is important to keep bones strong, as well as the muscles supporting them.
Niki Bezzant is a food and nutrition writer and speaker. Follow Niki @nikibezzant