Did you know that calcium is the 5th most common substance in your body and the most abundant mineral? You probably know that a large part of your bones and teeth are made up of calcium. But calcium plays a much bigger role in health than contributing to strong bones and teeth, and these functions are all of importance to someone taking part in endurance sports like running, cycling and triathlon. For example, adequate calcium is needed to enable the contraction of heart muscle which in turn pumps blood around your body. It’s also required in the process by which your skeletal muscles contract. It helps nerve signals to be transmitted and it’s essential for normal blood clotting when injury occurs. It is also needed to activate the enzyme lipase which breaks down fat stores to produce energy.
As an athlete, you need to ensure that you are getting adequate calcium. That’s 700mg a day for adults and 800-1000mg for teenagers who are still growing. For most people, it’s perfectly possible to gain all the calcium you need from the foods in your diet. If you consume dairy products, you can cover you can cover your calcium needs with 2-3 servings per day of milk, yogurt or cheese. Not only is calcium relatively high in these types of foods but it is also in the form that is relatively well absorbed by the body compared with the calcium found in plant foods. But it is perfectly possible to meet your calcium requirements from non-dairy sources; you just need to ensure that you include a range of different foods in your diet each day.
The following foods are the best non-dairy sources of calcium: tofu, dried figs, canned fish with soft bones (eg salmon, sardines), kale, broccoli, collard and mustard greens, pak choy, chickpeas (garbanzo beans), kidney beans, white beans, lentils, sesame seeds (or tahini paste), chia seeds and almonds. You’ll notice that spinach, which is often thought of as an useful source of calcium, is missing from the list. This is because spinach is particularly high in a substance called oxylate which reduces absorption of calcium. Another substance that adversely affects calcium absorption is phytate, found in many plant foods and especially legumes, nuts and seeds. Phytates bind minerals in the digestive tract so prevent them from being fully absorbed. This limited ‘bio-availability’ of calcium in plant foods means that you need to choose several different foods on the list above to meet your calcium requirements if you don’t consume dairy products. If you are choosing non-dairy milk, eg soya, coconut or almond, choose one that has been fortified with calcium; the same with tofu. It’s also important to mention that calcium absorption is reduced by plant tannins, which are found in teas, so don’t have all your milk with tea.
Some endurance athletes fail to get enough calcium in their diet. This might be because their overall calorie intake is too low to meet their energy needs or specifically because they don’t eat enough of calcium-rich foods. As a consequence, they may develop a condition called osteopenia where bone mineral density is lower than expected. If left untreated, this can develop into full blown osteoporosis with increased bone fragility and increased risk of fractures. Female athletes who have low oestrogen levels because they have developed amenorrhoea (loss of menstrual periods), which increases bone loss further, are at greater risk of osteopenia and need extra calcium, usually in the form of a supplement.
According to Dr Nicky Keay, a Sports Endocrinologist (www.nickykeayfitness.com),
Relative Energy Deficiency in Sports (RED-S) is caused by inability for intake to meet both training demands and “housekeeping” activities in the body. This situation of relative energy deficiency, ie an inadequate energy intake from food, results in multiple effects on hormone function, including sex steroids (low oestrogen in women and low testosterone in men), which may adversely affect bone health. Certainly, calcium as part of periodised nutrition to match training demands is important to restore normal hormonal function, which supports all aspects of health and sports performance. These considerations are of particular importance for young athletes who have higher energy and nutritional demands, on top of training demands. Inability to attain peak bone mass (PBM) during adolescence can result in impaired bone health moving into adulthood. See here for more details. But just optimising calcium intake, whilst important, will not remedy the situation. See this blog post for more nutritional tips on how to avoid or recover from RED-S
It’s also important to bear in mind that calcium is one of the minerals lost in sweat. This can contribute to reduced bone density due to the consequent disruption of parathyroid hormone if not addressed. Using an electrolyte or energy drink which includes a range of minerals including sodium, calcium, magnesium and potassium is appropriate on your longer training session or when hot conditions lead to increased sweating. In longer term signs of calcium deficiency include heart palpitations, raised blood pressure, joint aches, tooth decay and brittle nails. The body attempts to restore calcium levels by “raiding” calcium stores in bone, rending the bones weaker.
Taking a calcium supplement, particularly if you already take a multivitamin that contains some calcium or regularly use electrolyte drinks, isn’t something I’d encourage unless you’ve been diagnosed with osteopenia or osteoporosis or possibly if you are post-menopause, when oestrogen levels are reduced. Excessive calcium intake is known to interfere with the absorption of other minerals, particularly iron, magnesium and zinc, all of which are particularly important for athletic performance. It’s also important to realise that calcium isn’t the only nutrient required for healthy bones. Protein, vitamin D, magnesium, vitamin C, vitamin K and vitamin E also contribute to the process of building and maintaining bone, working in conjunction with calcium. A higher protein intake also improves calcium absorption.
So, to support your endurance sports performance and reduce the risk of low bone mineral density, which might contribute to injury, be conscious of meeting your daily calcium requirements. Here’s a table to help you. It shows the amount of calcium in some of the foods mentioned above:
|Food and serving size||Amount of calcium in serving|
|Steamed tofu, with added calcium, 100g||500mg|
|2 tinned sardines with bones||247 mg|
|Milk, 200ml||240 mg|
|Soya milk with added calcium||240mg|
|Low fat yogurt, 125g||220 mg|
|Cheddar cheese, 25g||175 mg|
|Dried figs, 2||125mg|
|Kidney beans, 4 tbsp||110mg|
|Tinned salmon, 100g||90mg|
|Chickpeas, 4 tbsp||70mg|
|Pak choi, 80g||65mg|
Jo Scott-Dalgleish BSc (Hons) is a BANT Registered Nutritionist, writing and giving talks about nutrition for endurance sport. Based in London, she also works as a Registered Nutritional Therapist, conducting one–to–one consultations with triathletes, distance runners and cyclists to help them eat well, be healthy and perform better through the creation of an individual nutritional plan. To learn more about these consultations, please visit www.nutritionforendurancesports.co.uk