Eat citrus fruit for strong bones
A diet with lots of orange and grapefruit may well reduce the chance of osteoporosis. Researchers at Texas A&M University did an animal study and discovered that adding orange and grapefruit to the diet had a positive effect on bone health.Study

The researchers did experiments with one-year-old male rats. This is the age at which rats are normally in the prime of life and therefore have no problems with weakening bones. The researchers had performed an operation to halt the production of sex hormones [ORX]. This made the rats resemble women in whom the estradiol production has stopped after menopause, or older men whose testosterone production has declined.Sex hormones like estradiol and testosterone play a prominent role in bone health.
Rats in the control group were also operated on, but their hormone production was not interfered with [Sham].
Some of the ORX rats were then given freshly squeezed orange juice to drink for 60 days [OJ; ORX+Orange]. Another group were given freshly squeezed grapefruit juice [GJ; ORX+Grapefruit]. The researchers squeezed the juice themselves, and there was a reason for this: analyses show that citrus fruits contain a number of bioactive substances. These are the limonoids, and they are found in juice you squeeze yourself, but not in ready-made juices you buy in cartons in the supermarket.
At the end of the 60 days, the Texans examined the bones of their lab rats. They saw that the decrease in bone density was smaller in the rats that drank citrus juice.

Stopping the production of the sex hormones made the bones weaker. They took less force (N) to break, and they broke more quickly. Supplementation with orange juice and grapefruit juice reduced this deterioration.

When the researchers examined the rats' urine they discovered that there was less hydroxyproline in the urine of the OJ and OG group rats. The concentration of the enzyme ALP in the blood of these two groups was also lower. Both of these are indicators of less bone decay.
"Orange and grapefruit juices positively affect serum antioxidant capacity and bone strength and delay the femoral fracture rate", the researchers conclude.

Nutrition. 2006 May;22(5):559-63.