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Nutrition and Performance in Sport

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Christophe Hausswirth

Chapter 2. Nutrition, sport and health

Topic 6. Bone health

Christophe Hausswirth, Amélie Fosse, Axel Heulin, Yann Le Meur, Véronique Rousseau, Eve Tiollier et École Lenôtre

Texte intégral

Questions and answers

1Key points

Regular physical exercise before the bones have fully matured can increase bone mass.
Intense and unfamiliar training in untrained athletes can lead to bone demineralization and stress fractures.
Calcium deficiency can jeopardize bone health, as this element is resorbed from the bones to maintain normal blood calcium levels.
Vitamin D deficiency causes inadequate bone mineralization, or even demineralization, and thus, weakens bone health.
A high-protein diet is associated with an increase in bone mineral density and a decrease in bone mass reduction.
There is a positive correlation between a low-acid diet, or even an alkaline diet, and a higher bone density.

What is “bone health”?

2The expression “bone health” refers to the bone’s resistance and its ability to resist fractures due to a fall, blow, torsion, or any other mechanical stress to which bones can be subjected. The notion of bone mineral density is associated with bone health. Bone mineral density is used as an indicator of the bone’s resistance to mechanical stress, to detect bone disease and follow-up treatment. When bone mineral density increases, its resistance also increases.

How do bones adapt to physical activity?

3The regular practice of certain sports has a direct effect on bone resistance; it can contribute to reducing the risk of fracture by 20 to 35%. Indeed, the healthier the bone tissue, the more adaptable it is to the mechanical constraints associated with muscle contraction: this makes it more solid and, at the same time, less subject to fractures. The load borne by the bone during physical exercise varies depending on the type of movement, its speed, power and the number of repetitions. However, performing only one exercise, even if it is intense or prolonged (isometric exercise), does not lead to bone adaptation, contrary to what happens with repeated exercises. To maximize bone health, it is essential to include diverse physical activities in the daily training schedule.

4Physical activity and better bone health are closely linked, since most exercise leads to an increase in bone mineral density, regardless of age. In addition, there is a very strong positive correlation between bone mineral content and the weight of the corresponding muscle. The important role of mechanical solicitation was shown by the results of a study involving ten professional tennis players. Bone mineral content was found to be an average of 15% higher in the radius of the racquet arm.

5The increase in bone density induced by physical activity is influenced by the level of calcium intake. However, this relationship is not linear, with a threshold effect observed at about 800 to 1000 mg.d−1 of calcium intake. Below this level, the effect on bone density is reduced; above, the increase in calcium intake does not have any additional effect.

Is there a difference between men and women in terms of bone growth?

6Regularly practising a weight-bearing sport has beneficial effects on bone health, both in men and women, and throughout life. Bone growth continues until the age of 20 in women and until the beginning of their thirtieth year in men, but it is before and during puberty that the greatest increase in bone mass is measured. Both in boys and girls, mineral density increases with size and body weight. As it is closely linked to the processes of sexual maturation, the peak of increase in bone mineral content occurs at age 11 or 12 in girls and about 18 months later in boys. Although adult women have a lower bone mass than men, this is more due to the difference in size and bone geometry than to the bone density itself. In general, a young skeleton is more sensitive to the mechanical stimuli provided by physical exercises than an older skeleton. Before puberty, practising sports with jumps or impacts plays a key role, because it maximizes the bone mass peak, hence generating enhanced and lasting resistance.

7The positive effects of physical activity on bone health were essentially shown when this activity was both remote in time and of an appropriate intensity. Conversely, intense training without appropriate preparation can lead to bone demineralization. This phenomenon was first observed in women and seems to be partially linked to the influence of training on hormonal status. In young women in particular, intense sport increases the prevalence of amenorrhea, which is associated with low plasma oestrogen levels. This favours accelerated loss of bone calcium. Athletes with amenorrhea thus have a lower bone mineral density than athletes with eumenorrhea, however, this is generally reversed when menstruation is restored.

Is there any correlation between the sport practised and bone health or calcium intake?

8Several transverse studies involving athletes (both men and women) practising a wide range of sports showed that, in this population, the bone mineral density (BMD) values were higher than in a population not practising sports. This was even more marked in those practising strength sports, in gymnasts and footballers. In contrast, sailing, running, swimming, diving or synchronized swimming are considered high-risk sports in terms of bone health. These differences are greater in female athletes.

9Specific case: given their beneficial effect on optimizing and maintaining bone mass in young athletes, physical activities involving a high-intensity load on the skeleton are highly recommended. However, in some cases these beneficial effects do not appear, for example, when there is hormonal insufficiency, nutritional deficiencies or an “overuse” syndrome. There does not appear to be any significant correlation between activity indexes and calcium consumption. This observation seems to invalidate the hypothesis whereby energy expenditure increases the calorie ration, which in turn influences calcium intake. This absence of correlation between the calorie intake and calcium intake results from very marked differences in eating habits, depending on the sport practised. Thus, athletes with a low calcium intake tend to compete in individual sports with high energy expenditure (triathlon, long-distance race or cycling), whereas athletes competing in team sports with high energy expenditure (volleyball, handball or basketball) tend to have a high calcium intake. In other disciplines, such as golf or horseriding, where energy expenditure is moderate, competitors say they consume a lot of calcium-rich products. It thus seems that the type of sport really does influence calcium consumption.

Do calcium and vitamin D contribute to better bone health?

10The key role played by these nutrients in bone health is now well known. Calcium is mainly involved in the formation of bones and teeth. Although it is a crucial intracellular messenger, 98% of the calcium present in the body is in the skeleton. Calcium deficiency jeopardizes bone health, since calcium is resorbed from the skeleton to maintain a normal blood calcium level. This demineralization can cause bone mass reduction, osteoporosis and a higher risk of fractures, especially when it is associated with a low-calcium diet, which goes hand in hand with low vitamin D levels. Dairy products should provide two thirds of the daily calcium intake; a diet low in dairy products provides only 500 mg of calcium per day, which is insufficient. However, when calcium intake is too high, (above 2500 mg.d−1), it can lead to the appearance of kidney stones. This is mainly a problem associated with calcium provided through supplements.

11The best-known function of vitamin D is the hormonal regulation of blood calcium and phosphorus concentrations. This function is important, since it ensures the availability of these minerals for bone mineralization and development. The active form of vitamin D stimulates calcium and phosphorus absorption in the intestine, reabsorption of calcium in the kidneys and the resorption of calcium from the skeleton, to preserve blood calcium levels. By maintaining calcium and phosphorus levels in the blood, vitamin D favours growth and bone health, as well as dental health. Therefore, vitamin

12deficiency leads to insufficient bone mineralization or to demineralization, and thus to poorer bone health. However, excessive vitamin D intake (more than 10000 UI per day) can damage the kidneys and other tissues. Any attempt to increase intake above the Dietary Reference Intake for vitamin D must raise this question: is the intake provided through food and drinks sufficient? A recent evaluation of vitamin D status showed that the serum level is generally sufficient to maintain good bone health. Nevertheless, athletes practising winter activities only indoors and who are not exposed to sunlight or outdoor light for at least 20 minutes per day may be at risk of deficiency.

What foods are good sources of calcium?

13The best calcium sources are foods from the “milk and dairy products” group. Other foods also contain this element in non-negligible amounts, especially some green vegetables, and calcium-enriched food.

14However, many vegetables, although they contain large amounts of calcium, are not good substitutes for dairy products. Indeed, for the bones and the rest of the body to benefit from calcium, it must first be absorbed from food. Most vegetables contain large amounts of oxalic and phytic acids, which chelate calcium and hinder its absorption. For example, after cooking, spinach contains 129 mg of calcium per 125 ml (half cup); this is much higher than the calcium content of most other foods (apart from milk – which contains 315 mg – and other dairy products), but it is estimated that only 5% of the calcium found in spinach is absorbed, i.e. only 6 mg. This is not much when compared to milk, from which 32% of the calcium is absorbed (i.e. 101 mg). Given the differences in calcium absorption, it would be necessary to eat 15 portions of spinach to get as much calcium as provided by one portion of milk! This is why, among food, dairy products are the most relevant when seeking to meet the daily calcium requirements. However, green vegetables should nevertheless be eaten as they contain many other minerals and vitamins necessary to a balanced diet.

15It is also important to understand that the Dietary Reference Intake was determined based on the calcium content of food, assuming that 30 to 40% of the available calcium is absorbed, on average.

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What factors influence endogenous vitamin D synthesis?

  • latitude

  • time spent outdoors

  • skin pigmentation

  • age

  • use of sun screen

  • clothing

16In countries located above a latitude of 40° north or below 40° south, UVB rays are not strong enough to promote endogenous vitamin D synthesis during the darker months. In addition, people who do not spend at least 20 minutes per day outdoors are vulnerable to vitamin D deficiency all year long.

17Melanin, a skin pigment, can reduce vitamin D photosynthesis by up to 50-fold. This is why people with darker skin have a higher risk of vitamin D deficiency. Endogenous vitamin D synthesis also decreases with age. Finally, a sun screen with a solar protection factor (SPF) of 8 or more also prevents endogenous vitamin D synthesis.

How can vitamin D nutritional status be improved?

18Since continuous endogenous synthesis is not easy to maintain, it is important that a good vitamin D nutritional status be maintained. This depends on the body’s vitamin D stores and on dietary intake.

19Only a few foods naturally contain vitamin D (for instance, fatty fish, egg yolk and fish liver oils), but these tend not to be consumed regularly.

20The table below lists good sources of vitamin D.

Fish and other food

Portion (g)

Vitamin D amount per portion (UI)

Salmon

75

204–392

Halibut, trout, herring

75

144–192

Tuna

75

105

Egg

75

52

Milk and substitutes

Portion (ml)

Vitamin D amount per portion (UI)

Natural milk

250

104

Powdered milk

250

104

Is vitamin K important for bone health?

21Vitamin K is a fat-soluble vitamin. Therefore, our body can store it in adipose tissues and in the liver. It is mainly known for its role in blood coagulation, but it also has a major impact on bone health. Vitamin K deficiency is not common, since it is present not only in green leafy vegetables, but can also be produced by bacteria in our intestine. However, taking antibiotics can sometimes kill off these bacteria, leading to a slight deficiency. The main symptoms of this are excessive bleeding of the gums or nose.

22Good food sources of vitamin K are beef, green tea, turnip, spinach, cabbages (particularly broccoli and kale), asparagus, and dark leaf lettuce, since chlorophyll contains vitamin K. Interestingly, freezing food can destroy this vitamin, whereas cooking does not affect it.

23Several studies have already shown that vitamin K has a beneficial effect on healing after fractures thanks to its role as intermediate in mechanisms including bone turnover. Nevertheless, its impact on the healthy skeleton remains controversial. Some Japanese researchers performed a meta-analysis on all existing data to assess the effects of vitamin K supplementation on women’s bone health. They retained seven studies with cohorts of at least 50 women taking vitamin K supplements, containing 200 μg to 5 mg per day of vitamin K1, or 45 mg per day of vitamin K2. Vitamin K1 constitutes 90% of vitamin K and is contained in green vegetables, whereas vitamin K2 is found in meat and fermented cheeses. The conclusion of the meta-analysis was that vitamin K supplementation is associated with improved bone density and a decreased impact of fractures.

24Spanish researchers have also shown a link between vitamin K and bone quality. They noticed that older people with a high vitamin K intake had a higher bone mineral density (BMD) than those with a lower dietary intake. The results mention an average daily intake of 334 µg in men and 300 µg in women, they also show that each increase of 100 µg in this daily consumption is accompanied by an 0.008 g/m2 increase in bone density.

Do proteins have an effect on bones?

25Most epidemiological studies investigating bone mineral density or the rate of bone loss show that a high-protein diet leads to an increase in BMD and a decrease in the rate of bone loss. A comparison between female athletes consuming large amounts of proteins (1.6 g.kg−1.d−1) and non-athletes who consumed less protein (0.8 g.kg−1.d−1) showed better bone health in the first population. Thus, an appropriate protein intake is essential to maintaining athletes’ bone health and preventing the risk of fractures. As a consequence, it is recommended that vegetarian athletes be carefully monitored, because with this diet, calcium, vitamin D and protein intake can be insufficient. Indeed, several recent studies show that vegetarian athletes have a lower bone density.

Can food acidity have an impact on bone health?

26Acid and base are produced in variable proportions during digestion depending on the food eaten. Acidifying food – which decreases pH – generates most organic acids (methionine, cysteine). Foods with this effect include animal proteins (meat, fish, chicken, seafood and eggs), cheeses and cereals. For a few years now it has been recognized that an excessive acid intake leads to the mobilization of the bone buffer system, which regulates pH by neutralizing excessive acid. There is thus a positive correlation between a low-acid diet and a higher bone density. Several studies conclude that adapting the diet over a long period could contribute to decreasing the risk of osteoporosis, regardless of whether physical exercise is performed. Similarly, a less acidifying diet (containing less meat and cheese, and more fruit and vegetables), completed with bicarbonate-containing water (which increases pH), reduces the level of urinary calcium and the bone resorption indicators, and has a positive effect on the individual’s bone health.

Practical applications

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1. Maintain your calcium intake

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Sources of calcium

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Main and secondary sources

Image 10000000000004000000013A6D8755F8.jpg

Image 10000000000000230000001FF40663F8.jpgRemember that milk puddingsImage 1000000000000027000000328384A6A9.jpg do not contain much calcium and are very sweet. Soy milk cannot be substituted for cow's milk. It is not recommended because it contains a high level of phytoestrogens.

To reduce loss of calcium

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2. Maintain your vitamin D intake

27 Main food sources of vitamin D

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28 For athletes exercising indoors, favour dairy products with added vitamin D and monitor status regularly using blood tests

29 Don’t forget that sun exposure is essential for vitamin D synthesis. Expose your forearms and face to sunlight for at least 20 minutes every day

3. Eat plenty of vegetables

30 To neutralize acidity (alkaline food)

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31 Take advantage of their antioxidants

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4. Maintain an adequate protein intake

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5. The female athlete triad

32 Definition

33 Intense exercise increases the risk of amenorrhea in young women, which accelerates the loss of calcium from the bones

Image 100000000000011B000000BDB34956C3.jpg

34 Sports for which this is the case

35 Sports where energy expenditure is high:

36– running, rowing, etc.

37 Sports with aesthetic constraints

38– gymnastics, ballet, synchronized swimming, etc.

Image 100000000000002900000023AD0F56EF.jpg If amenorrhea occurs, consult a doctor as soon as possible.

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Recipe

Halibut "en papillote", fennel compote

Image 100000000000014B0000015F9CDC47A7.jpg

Image 10000000000001E7000001E7B6E5D4EC.jpg

Photo credit: Thibaut Ruggeri.

39Serves 2

40Preparation time: 40 minutes

41Cooking time: 15 minutes

Difficulty: Image 10000000000000560000002034F64BB8.jpg

42Ingredients

43 280 g halibut fillets

44 100 g tomatoes

45 1 lime

46 10 g olive oil

47 2 sprigs of lemon thyme

48 Mild chilli pepper

49 10 g peeled garlic

50 80 g onions

51 300 g fennel bulb

52 5 g olive oil

53 Salt, pepper

54Peel and chop the onion.

55Wash the fennel, cut it in two lengthwise and slice thinly.

56Sweat the chopped onions and crushed garlic in olive oil. Add the sliced fennel.

57Season, cover and leave it to cook.

58Once it is fully cooked, transfer to a dish and set aside.

59Wash the tomatoes and slice them.

60Remove the zest from the lime, cut it in two and squeeze it.

61Cut two pieces of foil. Place half the sliced tomato in the centre of each piece of foil.

62Divide the cooked fennel and place on tope of the tomatoes. Top with the halibut fillets. Add salt and pepper, a sprig of lemon thyme, a pinch of chilli, drizzle with olive oil and the lime juice, sprinkle with the zest.

63Close the papillote and tie with string or a piece of raffia.

64Bake in the oven at 180 °C for 15 minutes.

65Serve in a deep plate.

66Chef’s note

67This dish covers 150% of the Dietary Reference Intake for vitamin D. It is also very rich in proteins.

68As it does not contain much carbohydrate should be served with a carbohydrate-rich starter or dessert. Since vitamin D promotes calcium absorption, it would be wise to add a dairy product (yoghurt, fromage blanc, yoghurt drink, etc.).

69Nutritional analysis per person

Energy (Cal)

Carbs (g)

302

13

Lipids (g)

Protein (g)

14

31

Rice pudding with pear and caramel

Image 10000000000001EB000001E548F7B29B.jpg

Photo credit: Thibaut Ruggeri.

Image 100000000000017400000155F54F42DA.jpg

70Serves 2

71Preparation time: 40 minutes

72Cooking time: 20 minutes

Difficulty:Image 100000000000002E0000001F7C6C0379.jpg

73Ingredients

74 60 g round-grain rice (Arborio)

75 500 ml semi-skimmed milk

76 Half a vanilla pod

77 Zest of half a lemon

78 90 g granulated sugar

79 2 egg yolks

80 50 ml single cream

81 2 tablespoons of water

82 Half a pear

83Pour the milk into a saucepan. Split the vanilla pod in two lengthwise and add to the milk.

84Bring to the boil and add the rice. Cook on a low heat, stirring regularly for 30 minutes. Once the rice is cooked, add 20 g of granulated sugar and the lemon zest.

85Pour into a glass bowl.

86Mix the egg yolks and single cream. Pour this mixture onto the rice and stir it in with a spatula. Set aside.

87Place the remaining granulated sugar in a saucepan with the water. Cook until the caramel turns light brown. Pour into an ovenproof dish.

88Peel the half pear and dice it.

89Pour the rice mixture onto the caramel, add the diced pear and bake in the oven at 200 °C for 20 minutes.

90Take the dish out of the oven and allow to cool.

91Chef’s note

92This dessert covers 40% of the calcium requirements and 20% of the vitamin D requirements for the average adult.

93It is quite rich; it should therefore be served with a light dish. Because it is high in protein and carbohydrate, you can also eat it as a snack after intense exercise with a high level of muscle solicitation.

94Nutritional analysis per person

Energy (Cal)

Carbs (g)

436

69

Lipids (g)

Protein (g)

12

13

Auteurs

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