Recently I attended a seminar which concentrated on bone health in women going through the menopause. The decrease in blood serum oestrogen after menopause is associated with bone loss and subsequent brittle bones and osteoporosis.
A study(1) was briefly mentioned at the seminar which seemed to suggest that onion consumption was linked to bone health in peri- and post-menopausal women. I was intrigued! The study found that individuals who consumed onions once a day or more had an overall bone density that was significantly greater than individuals who consumed onions once per month or less. This association was apparent even after the authors took various other factors (that can affect bone health) into account such as age, body mass index (BMI), daily calcium intake, serum vitamin D, serum parathyroid hormone, oestrogen use, smoking status, and exercise status. This suggests that onion consumption may be an independent factor in bone health. The study also found that older women who consume onions most frequently may decrease their risk of hip fracture by more than 20% versus those who never consume onions.
Why would onions be having this kind of effect? A possible explanation could be that onions contain a flavonoid (bioactive plant compound) called quercetin which has antioxidant and anti-inflammatory actions in the body and has been linked with protecting against heart disease, cancer and asthma. Quercetin is also found in apples and grapes. Two laboratory studies (2,3) last year found that quercetin could increase new bone formation.
Quercetin is also classes as a phytoestrogen. Phytoestrogens are natural plant-derived compounds that bind to oestrogen receptors and have oestrogen-like activity in the body. Recently phytoestrogens have attracted much attention among public and medical communities because of their potential beneficial role in prevention and treatment of cardiovascular diseases, osteoporosis, diabetes and obesity, menopausal symptoms, renal diseases and various cancers.
Our bone cells (osteoblasts) have two oestrogen receptors on their surface and certain phytoestrogens, including quercetin, can interact with these oestrogen receptors in bone. It is possible that quercetin binds to the bone oestrogen receptors and stimulates and increases bone formation and bone mineralisation. Further studies are needed to investigate these ideas. The authors of one of the studies say (3)“If quercetin, this common constituent in fruits and vegetables, can be shown to increase bone forming activities in bone cells and improve healing in bone defects, it may be the long-sought-after safe and ideal agent for stimulation of bone formation and bone defect repair”
Onions are one of my favourite vegetables and easy to integrate into meals and salads. Apples and grapes are also easily incorporated into the daily diet. Last year I wrote about the importance of fruit and vegetables for bone health. A number of studies over the last decade have suggested a clear, positive link between fruit and vegetable consumption and bone health. These foods provide a huge range of nutrients that are important for bone health. In addition to the nutrients, fruit and vegetables positively effect the pH balance (a measure of acid-alkali balance) in the body, by increasing the alkalinity in the body (making the body less acidic), which plays a major role in the prevention of calcium loss from bones. Foods which are acid forming in the body include foods such as most meat and animal protein, cheddar cheese and many grain products e.g. white bread, pasta, cornflakes. If the body is too acidic, and not in pH balance, then bones can release their calcium (which increases alkalinity) into the blood to try and maintain the balance. Obviously calcium loss is not what we want!!
Providing the body with abundant supplies of vegetables and fruits, especially those high in quercetin, may help to keep our bones strong as well as protecting us from many other diseases. Quercetin supplements are also readily available to buy, usually as an antioxidant boost for the body and for allergy prevention and treatment, although their impact on bone health have not yet been tested.
Please also read my other various posts on osteoporosis for more information on how to keep bones healthy
(1) Matheson EM et al. 2009. The association between onion consumption and bone density in perimenopausal and postmenopausal non-Hispanic white women 50 years and older. Menopause. 16(4):756-9.
(2) Wong RW & Rabie AB. 2008. Effect of quercetin on bone formation. J Orthop Res.26(8):1061-6.
(3)Wong RW & Rabie AB. 2008. Effect of quercetin on preosteoblasts and bone defects. Open Orthop J. 10;2:27-32.
Written by Ani Kowal
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