Many people who take vitamin pills every day think they are improving their health. If it's the right kinds, they may be, but if they are getting too much vitamin A it can damage bone health and increase the risk of hip fracture.
Excess vitamin A seems to stimulate osteoclasts (scavenger cells that break down bone) and suppress osteoblasts (cells that build up bone). High levels of vitamin A also interfere with vitamin D, which is crucial for calcium absorption and metabolism.
Researchers analyzed data from the Nurses' Health Study to find the relationship between intake of vitamin A and hip fracture rates in 72,337 postmenopausal women followed for 18 years. They divided the women into five equal groups from lowest intake of vitamin A to highest intake. Those who had the highest intake (top 20 percent) of vitamin A had a 48 percent increased risk of hip fracture, compared to women with the lowest intake (bottom 20 percent). It's also interesting to note that the average age for hip fractures was only 64 years.
Vitamin A Comes from Two Sources
Retinol is the form of vitamin A that comes from animal sources – liver, egg yolk, oily fish such as cod liver oil and sardines, whole milk, butter, and cheese. Retinol is also added to many foods including margarine, breakfast cereals, skim milk, cheese, and vitamin supplements.
Beta-carotene is the other vitamin A source. It comes from highly colored plant foods such as carrots.
When comparing the two sources, only retinol was significantly associated with hip fracture risk. If you compared dietary intake of only retinol, those eating the most (top 20 percent) had nearly twice the risk (1.9 times) of hip fractures compared to those eating the least (bottom 20 percent).
How Much Is Too Much?
Those women who had the lowest rates of hip fractures consumed less than 500 micrograms of retinol daily. If you also included beta-carotene, the intake of vitamin A (called retinol equivalents) was less than 1250 micrograms daily (which is equivalent to a little over 4,000 IU of vitamin A daily). The current recommendation for vitamin A is 700 micrograms per day for women (a little more for men).
Those with the high risk of hip fracture were eating about 2000 micrograms of retinol per day, or with the added beta-carotene, over 3000 retinol equivalents daily (or about 10,000 IU of vitamin A). The current upper limit for safe intake is less than 3000 micrograms per day, so about 20 percent of the women in the study were exceeding this upper limit.
Most of the vitamin A (retinol) in these women with the high intake was coming from ordinary vitamin pills.
Here Is the Bottom Line
To prevent hip fractures, limit your retinol intake to less than 500 micrograms (1650 IU) per day. Get the rest of your vitamin A needs from beta-carotene (brightly colored fruits and vegetables), which has many protective health benefits and doesn't increase the risk of hip fractures.
If you take vitamins with vitamin A in them, make sure it comes primarily from beta-carotene and not retinol (if it doesn't say, it's most likely from retinol). If your intake is high, as it was in 20 percent of the women in this study, following these new guidelines has the potential of cutting your risk of a hip fracture in half. |
