Chocolate and Chocolate constituents influence bone health and osteoporosis risk
The following is a summary of the stated research mentioned above. The content summarized here, including the figures and tables, all belong to the researchers (unless otherwise indicated). The summary attempts to stay as close to the original paper as much as possible with some adjustments in regards to jargon, length, or to focus on bean to bar aspects.
Introduction
Chocolate has been considered a functional food (nutraceutical) throughout its history, but particularly in the last decade or so. This is especially true for the current bean to bar craft chocolate industry.
The functional food component of chocolate tends to focus mostly on polyphenols (antioxidants), however other nutrients are contained within chocolate such as:
carbohydrates
lipids
dietary minerals
oxalates
methylxanthines (such as caffeine)
These can positively or even negatively influence diet-related chronic diseases.
Osteoporosis is a degenerative skeletal disease which can weaken bone density, making bones frail, and more susceptible to fractures. It’s caused by an imbalance between bone formation and resorption (degradation in our case here). About 1 in 3 women, and 1 in 5 men suffer from osteopenia worldwide. Osteopenia is bone density loss that is worse than normal healthy bone, but not as advanced as osteoporosis.
The intake of specific kinds of flavonoids may promote bone health. Cocoa solids (the non-fat portion of a cacao bean, which is used to make chocolate) has the highest flavanol content of all foods on a per-weight basis. It is higher in flavonoids than tea, or high flavonoid fruits and vegetables.
Fun Fact: Who consumes the most chocolate? The Swiss beat the record, consuming on average 9 kg/year per person! This equates to about 209 43 g (1.5 oz) chocolate bars. Americans consume about 4.3 kg/year. It is estimated About 15% of women between 40-49 years of age consume chocolate about once every three days.
Those at risk for osteoporosis lose bone or bone density at a rate of about 0.2% to 0.5% per year after the age of 40-45. However, this rate of bone loss increased to 2-5% after menopause.
The study here wanted to observe the potential role of consuming chocolate in regards to bone health.
Biological Plausibility
Below is a list of known information that help lead to this look into chocolate and how it relates to bone health.
A study in Scotland on 5119 postmenopausal women (aged 45-54) associated flavonoid intake with higher hip and lumbar spine bone mineral density. The flavonoids were consumed mostly through tea drinking (57%). Catechin was identified as the main flavonoid consumed. [24]
Cocoa beans are comprised of about 37% catechins. Epicatechin makes up about 35-43% of the phenolic content in chocolate.
Chocolate, being made from cacao beans, also contains high levels of both catechin and epicatechin even after cacao bean processing.
Antioxidant properties of chocolate (which fight against oxidative stress and inflammation) could have positive implications for bone health since chronic bone loss is accompanied by oxidative stress and inflammation.
Animal and human models have shown that reactive oxygen species (ROS) have a negative impact on bone health. ROS can affect the bones by:
stimulating osteoblast apoptosis (cell death) and senescence
upregulation of receptor activator of nuclear factor k-B ligand
to activate osteoclast differentiation
and bone resorption
In vitro, human osteoblasts cultured in cigarette smoke medium were treated with various doses of catechin, and saw a significant reduction in ROS (reactive oxygen species) formation.
Proinflammatory cytokines, interleukin (IL)-1, IL-6, and (TNF)-a are important regulators for bone resorption, and possibly play a role in age and estrogen deficiency-related bone loss. [31]
An in vitro study, adding TNF-a to osteoblastic MC3T2-E1 cells stimulated inflammatory cytokine IL-6, promoting osteoblast apoptosis [32]. Treating these ostoblasts with catechin reduced TNF-a concentration by 32%, and increased ostoblast survival by 43%, and increased alkaline phosphatase, a marker of osteoblast activity. The authors concluded the catechins preserved bone-forming osteoblasts by exerting anti-inflammatory actions.
A crossover study involving normal and hypercholesterolemic individuals, consuming cocoa powder with milk twice a day for 4 weeks significantly decreased serum inflammatory biomarkers for IL-1 compared to those who only drank milk.
These studies suggest that there is potential for chocolate and cacao to promote bone health.
Studies on chocolate consumption and bone health
The following information was taken from studies which have looked into various aspects of bone health and chocolate consumption.
Many of the studies have looked into chocolate milk as a way to increase calcium consumption in children, but didn’t include an information on bone health. [34]
Bone mineral accrual during childhood is a key determinant in future risk of osteoporosis. [10] Meaning, if the process of bone density, thickness, or length is hindered during development, this can increase their risk as older adults.
One study of 6-10 year old girls showed that calcium-supplemented chocolate bars, cakes, or beverages significantly increased height and bone mass acquisition in the radius and femur. This also resulted higher bone mass maintained 1 yr past termination of the intervention [35]. This study suggests chocolate may play a role in promoting bone mass in prepubertal girls. However, they point out the mechanisms to explain this require more investigation.
A preclincal study (meaning on animals) fed female mice a diet supplemented with 400 mg unsweetened chocolate during pregnancy and lactation. It resulted in offspring with significantly shorter forefeet and hind limbs [36].
A follow up study of number 4 above looked into the relationship of catechins and angiogensis and bone mineralization in the offspring who were fed chocolate. The authors suggested that the antiangiogenic activity of chocolate catechins disturbed the processes of bone elongation and mineralization [37]. Important note: The female mice were given 400g of chocolate daily, which is equivalent to 8.7 46 g chocolate bars!
A study on sedentary vs circuit training men who consumed a chocolate malt drink indicated that the men who were physically active showed lower levels of a bone resorption marker. The sedentary group showed no effect.
In contrast, a similar study on healthy young women undertaking aerobic dance and daily chocolate malt drink for 8 weeks saw no significance effects [39]
These differences appear to be due to sex differences. As well, the women drank the malt drink for a longer duration.
Healthy, overweight, or obese premenopausal women following an energy-restricted diet consumed a high flavanol cocoa beverage (280 mg flavanols/d) and 2 dark chocolate snacks (240 mg flavanols/d) for 18 weeks. However, the changes were not significantly different from the control group who didn’t consume the flavanol rich drink. Therefore, results indicate the beverage didn’t provide benefits to biomarkers of bone turnover, BMD, oxidative stress, and inflammation above that provided by weight loss.
A 5 year trial involving 1001 Australian women aged 70-85 investigated the effects of calcium supplementation on bone density and strength. The only impact appeared to be that tibia bone density and strength were lower in the women who said to have consumed chocolate daily vs those where consumption was rare [41]. Based on these results, the authors concluded that daily chocolate consumption increased the risk for lower bone density and strength in postmenopausal women.
Those who consumed chocolate daily had a higher socioeconomic status and exhibited lower body mass index values despite greater total caloric saturated fat, total carbohydrate, and sugar intake associated with chocolate
Other lifestyle factors such as activity levels were not monitored during the 5 yr intervention.
Limits of this study include reliance on self-reporting chocolate consumption, and not specifying the type of chocolate
Types of chocolate are important because they contain different levels of polyphenols depending on type and ingredients.
Chocolate polyphenol content
The term “cacao” is meant to refer to the raw unprocessed bean from the cacao fruit tree. “Cocoa” as in “cocoa bean” is the term used after the cacao bean has undergone processing in order to be able to be used in chocolate manufacturing.
Polyphenol content of the cacao is influenced by variety and genetics. Even within species, polyphenol content depends on growing region, climate during growth, maturity at harvest, and storage time [44].
Polyphenol content of cacao is about 10% dry weight. This makes cacao beans rich in pholyphenols.
Lee et al [18] reported cocoa contains higher total flavonoids per serving than red wine or black tea, and demonstrated the highest antioxidant activity in in vitro assays.
The flavanols in cocoa are mainly epicatechin and catechin. Polyphenols are also responsible for the bitter and astringent taste of cacao beans. To reduce this, cacao beans undergo processing.
Fermentation is the first major processing step which occurs. De brito et al. [48] reported a 24% decrease in total polyphenol content after 60 hrs of fermentation, and a 58% decrease after 8 dats of fermentation. Fermentation can result in an 80% reduction of catechin and epicatechin content.
After fermenting, cacao beans are dried to inhibit microbial growth. Drying had a minimal effect on epicatechin and catechin content.
The next step is roasting, generally at 100*C to 150*C as whole beans or as nibs (broken up beans with the testa removed). Roasting cocoa beans at temperatures above 70*C resulted in the loss of epicatechin. However, catechin content increased when roasting temperatures reached 120*C owing to increased epimerization of epicatechin to catechin!
Roasting plays an important role in forming aromas compounds. This is then ground into cocoa liquor (essentially a cocoa bean paste, similar to peanut butter), and then proceeded to make chocolate.
Cocoa powder and cocoa liquor can be modified with an alkali treatment AKA
”dutching”. This darkens the cacao and mellows out the flavour (reduces bitterness). However, this also had the greatest reduction in flavanols. It decreased catechin content by 80% and epicatechin by up to 98% [52].
Miller et al. compared products and found unprocessed cocoa powder was 34.6 mg/ 100g flavanol content compared to 13.8 mg in lightly alkalized cocoa, 7.8 mg in medium alkalized powder, and 3.9 mg in heavily alkalized powders. Polyphenol content was overall higher in less processed and less alkalized cocoa powders.
Results indicate that palatalization decreased the amount of flavanols, the total polyphenol content, and antioxidant activity. [50]
According to USDA [55] (Table 2 above) catechin content from highest to lowest included:
cocoa beans
cocoa powder
baking chocolate
alkalized cocoa powder
chocolate confections
Miller et al. [57] reported non-fat cocoa solids (the brown portion of cacao beans which contain most of the polyphenols and minerals) were highest in cocoa powder (72-78%), then dark chocolate (20-30%), semisweet (15-19%), and milk chocolate (5-7%). A 40 g bar milk chocolate has 394 mg polyphenol antioxidants, dark chocolate provides 951 mg!
This is why its important to note the type of chocolate consumed in studies, which many studies do not.
Other chocolate constituents
Chocolate isn’t all about flavonoid content, it also has many other constituents that can have an impact on health.
Even though chocolate is low in vitamins important for bone health, chocolate and cocoa is used in foods that are a source of vitamins A and D such as milk products.
Kuhn et al. [58] has suggested that food databases should be updated in regards to chocolate being a source of vitamin D (~ 4 ug/100g for dark, and ~2 ug/100g for milk chocolate).
Dietary Mineral Content
Overall, studies have shown that cocoa powder and high percentage dark chocolate (70% and up) can provide a source of minerals important to bone health. However, chocolate contains high amounts of oxalates (between 500-900 mg/100g). Oxalates may bind to minerals and reduce absorption into the body. This is something to consider when looking at levels of minerals in chocolate and cocoa powder. Read more about oxalates in another summary I did on chocolate and oxalates here.
Calcium
Many of you already think calcium when you think of bone health. It’s important to the mineralization (development) of the skeleton.
Hodgson et al. [41] conducted a study that showed no significant difference in women who ingested chocolate daily versus rarely. However, calcium content can range from 14 to 281 mg/100g depending on the type of chocolate, and the type of chocolate is rarely noted in many studies.
Generally, dark chocolate contains the highest amounts of minerals and polyphenols. However, when it comes to calcium, white chocolate contains the most, mostly due to the milk powder content. White chocolate is made of the fat from cacao, sugar, and milk powder. Dark chocolate (especially high quality dark) doesn’t contain milk (although cheaper brands may contain milk derivatives). White chocolate also contained the highest amount of sodium, which may influence calcium bioavailabilty.
In a trial study, postmenopausal women who were fed a high calcium and high sodium diet had a greater amount of calcium excreted in the urine, and negative bone calcium balance than women given lower amounts of both. [60]
Magnesium
This is also important to bone crystal growth, and tied to vitamin D parathyroid hormone axis [59]. A pooling of 12 studies found positive correlations between magnesium intake and femoral neck and total hip BMD (Bone Mass Density).
A typical serving of dark chocolate (44 g; 1.55 oz) provides 15% of the dietary allowance for adults [62].
The Hodgson study [41] showed that postmenopausal women who consumed moderate amounts of chocolate (1-6 cups per week) showed lower magnesium intake than those who consumed chocolate rarely. Of course, type of chocolate wasn’t indicated, and it can change depending on type of chocolate. Cocoa powder has the most magnesium, followed by dark chocolate, milk chocolate, and white chocolate with the lowest amount.
Copper
Copper is important to bone growth, as it inhibits bone resorption, and also helps in the development of collagen and elastin in bone [64]. A study of 722 male and female aged 45-68 whose blood serum (the yellow part) was low in copper, also had lower femoral neck and total femur BMD [65].
Chocolate contributes 9.4% of the daily copper intake for Americans [66]. Cocoa powder has the highest amount of copper, followed by dark, milk, and then white chocolate. Cocoa powder (15 g; 1 tbsp) provides up to 82% of the recommended daily allowance (RDA) for copper. Dark chocolate at 70% cocoa solids (28g) provides about 70% RDA, milk chocolate (44 g) 31%, and white chocolate (85g) only 7%.
Zinc
Zinc plays a structural role in bone formation [69]. A study of premenarchal girls (aged 9-11) who consumed zinc tablets saw an increase in the biomarkers for bone formation in their blood serum [70]. Another study on healthy men who consumed zinc supplements saw a marker of bone formation increase by 11% after 6 weeks [71].
As per usual, the greatest amounts of zinc were found in cocoa powder (15 g provides 13% RDA), then 70% dark chocolate (28g = 11%), milk chocolate (44g = 12.5%), and finally white chocolate (85 g = less than 1%).
Iron
Iron is important to collagen and bone formation [72]. A study on increased iron intake by healthy postmenopausal women showed greater BMD at all skeletal sites. Cocoa powder (15g) provides 12-26% of the RDA, 70% dark chocolate (28 g) provides 18-42%, milk chocolate (44 g) provides 22-48%, and white chocolate (85 g) provides less than 1%.
Fat Content
Fat (lipid) content of chocolate comes from the fat within the cocoa bean, milk powders in regards to milk chocolate, and vegetable oils in some commercial chocolate.
Fat content is highest in dark chocolate and white chocolate. Cocoa butter is composed mainly of three fatty acids:
Stearic acid (saturated)
Palmitic acid
Oleic acid (monounsaturated)
Some research appears to suggest that saturated fatty acids (SFA) may increase hip fracture risk [77]. Increased levels of SFA may include:
reduced calcium absorption
more calcium excreted in the urine
increased survival of osteoclasts (cells that break down bone)
inhibiting the development of marrow cells to osteoblasts
Hodgson et al. stated that postmenopausal women with daily or moderate chocolate consumption had higher fat intake overall versus women who only consumed chocolate rarely [41].
Sugar Content
Hodgson et al. stated that postmenopausal women with daily chocolate consumption had higher sugar intake overall versus women who only consumed chocolate moderately or rarely [41].
Sugar is added to reduce bitterness in lower quality cacao, but also to reduce intensity and also bring out aromas that may be masked without the addition of sugar.
Sugar content is highest in white chocolate, followed by milk, dark, and then unsweetened cocoa powder. Sugar may effect the bioavailability (how well your body absorbs nutrients) of other chocolate constituents. Studies on both humans and animals reported that consuming cocoa with sugar increases the bioavailabitly of flavanols (antioxidants) [80,81].
Very few human studies have looked into the impact of sugar on bone health. Preclinical studies (on animals) showed that higher sugar intake usually had a negative impact on bone health [82]. One explanation is that high sugar intake increases calcium excretion (via hyperinsulinemia) and thereby decreasing calcium re-absorption, which may lead to bone loss over time [83].
One study on healthy adults showed that consuming 100 g of chocolate daily reduced insulin resistance (due to the flavanols) [84]. However, the type of chocolate consumed was not available. Insulin resistance is a symptom of type 2 diabetes.
A study on postmenopausal women who reported moderate chocolate consumption (28 g 1.5-3 times per month) had a significantly reduced risk of diabetes. However, the women who consumed chocolate more than 3 times per week did not a reduced risk of diabetes [85]. Type of chocolate was not available.
A trial on healthy men received either high-flavanol dark chocolate or flavanol-free white chocolate for 15 days (controlled for equal levels of calories, macronutrients, cocoa butter, fiber, and minerals). The dark chocolate consumption reduced insulin resistance, indicating that the flavanols was the beneficial ingredient [87].
Methylxanthine
Caffeine, theobromine, and theophylline (not detected in cocoa beans) are methylxanthines. Methylxanthines stimulate the release of stored calcium from bones [88]. Since 99% of calcium in the body is stored in bones, high consumption of methylxanthines may lead to bone mineral loss.
Postmenopausal women who consumed chocolate daily showed negative impacts on bone health. The authors suggested methylxanthines were the contributing factor [41].
Caffeine has been shown to reduce calcium absorption and increase calcium excretion in urine [89,90]. Dark chocolate and cocoa powder had the highest level of caffeine, followed by cocoa powder, and then milk chocolate [91,92]. That said, chocolate contains very little caffeine compared to other more popular caffeine sources. Chocolate milk only provides 4 mg of caffeine while coffee provides about 85 mg, tea at 30 mg, and soft drinks at 18 mg [94].
Theobromine makes up about 2-3% of the cocoa bean weight, which is bioavailable and resists degradation during cocoa processing [88]. As well, theobromine levels in chocolate are higher than in coffee, tea, and carbonated beverages [91]. Theobromine was highest in dark chocolate, then cocoa powder, followed by milk chocolate, with white chocolate being below detection levels. In one study, theobromine levels ranged form 150 to 750 mg [93].
In one study, treating human bone marrow mesenchymal stem cells with theobromine promoted bone growth via osteoblast formation and mineralization [97]. Rats exposed to theobromine in utero daily until postnatal day 50 showed increased femoral length, cortical thickness, and trabecular thickness and number [97].
To the knowledge of the authors, no human studies looked into the link between theobromine consumption on bone health.
Theobromine is generally safe for human, and wouldn’t be considered toxic until levels of 18 g/ day, which is equivalent to 151 30 g chocolate bars a day [98]. However, the authors still suggest more studies in regards to theobromine on human health.
Conclusion
We have reason to believe chocolate and cocoa powder provide dietary source of flavonoids and other constituents with the potential to affect bone. However, the benefits in chocolate and cacao may be outweighed by other constituents which may have adverse effects on bone health.
Hodgeson et al. [41] reported inverse relationship with high chocolate consumption and lower BMD in postmenopausal women, while other studies showed no such effect. Also, adolescent girls showed greater longitudinal bone growth, and seemed to benefit by chocolate and cocoa consumption.
The osteogenic effects of chocolate depended greatly on the type of chocolate, which for most studies was not indicated. More research in human studies are needed, which specify the type of chocolate.
Determining dietary recommendations for chocolate consumption is important with an increase widespread and growing popularity of chocolate consumption.
