It’s yet another case of medical advice reversal. For years doctors have been urging healthy female patients to take supplements with calcium and vitamin D. Now a panel says the science doesn’t back it. A number of news outlets ran a story today, including Philly.com:
A leading U.S. government advisory panel has proposed that postmenopausal women not take low-dose calcium and vitamin D supplements daily to ward off bone fractures….The news was a bit of a bombshell, given that women have been told for so long to take calcium and vitamin D, said Dr. Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York City and a spokeswoman for the American Heart Association. "What we're really seeing is no role for calcium for the prevention of osteoporotic fractures. At this point, there's no reason to be taking calcium," she noted.
I took an evolutionary view of this issue last November. One reason we might need extra vitamin D is that the human race evolved in sunny, equatorial climates and we’re still not completely adapted to life in higher latitudes. Widespread vitamin D supplementation has been crucial in fighting a horrible bone-softening disease called rickets. But it’s not surprising that we can’t easily find a one-size-fits-all recommendation for optimal health, since levels vary so much by sun exposure, skin color and other factors. And our need for vitamin D has very deep evolutionary roots:
Why did evolution make us so high-maintenance and dependent on all these vitamins and minerals? That's a question that intrigued Michael Holick, a professor at Boston University School of Medicine. He found that it all started around 500 million years ago, just as complex organisms were starting to evolve.
Complex life started in the ancient seas that were rich with plankton. Plankton make Vitamin D from the sun so it infuses the food chain. While it's not clear what they needed it for, Vitamin D was everywhere and apparently useful, and so it became woven into the biology of the animal kingdom at its roots.
"We've looked at everything from zooplankton to brine shrimp to frogs and lizards," said Holick. They all need Vitamin D. Animals either make their own with sunlight, or they eat animals that contain it.
Nocturnal animals and polar bears get their D from their prey. Even vampire bats need Vitamin D, Holick said; it's in the blood they suck from other animals. Sheep make their own Vitamin D in their wool and then get it into their systems when they lick themselves.
Originally, humans made more than enough in skin, Holick said. When some of our ancestors left Africa, they adjusted their skin tone to allow in more sunlight. Penn State's Jablonski found that around the world, the skin color of native people maps almost perfectly onto a map of UV radiation; the more UV, the darker the average skin.
In 2005, Penn State professor Mark Shriver and colleagues isolated a genetic mutation that contributed to Europeans' having white skin, a mutation that in zebra fish leads to absence of the characteristic stripes.