Broccoli is just the thing to keep astronauts’ bones healthy

IF PEOPLE are ever to reach Mars or other planets, they had better take some broccoli plants with them. French researchers have found that a deficiency of vitamin K-which is particularly abundant in broccoli-may contribute to bone loss in astronauts.

Scientists have known that bone loss occurs in space, but the reasons have been unclear (New Scientist, 15 July, p 22). To try to understand the mechanism, a team from the Jean Monnet University at Saint-Etienne studied the biochemical markers of bone formation in the blood and urine of two cosmonauts on separate Mir space missions.

An important bone growth marker is osteocalcin, a protein that helps build bone. Osteocalcin needs vitamin K to undergo a process called carboxylation, which makes it bind to the mineral portion of the bone, causing bone growth. Vitamin K supplements have been shown to increase the carboxylation of osteocalcin, and reduce bone loss in post-menopausal women.

Under-carboxylated osteocalcin (uOC) cannot bind to bone and cause it to grow, so an increase of uOC levels in the blood gave the French team a useful marker. The two Mir cosmonauts showed dramatic increases in uOC within three to four days of being in microgravity. ‘We were very surprised. We thought the body has some stocks of carboxylated osteocalcin. Apparently this is not the case,’ says team member Marie-HÈlËne Lafage-Proust.

One cosmonaut was given vitamin K supplements during part of a 180-day space mission. Before taking the vitamin, his uOC levels were high compared with pre-flight levels, highlighting the effects of microgravity. But daily doses of vitamin K slashed the amount of uOC in his blood to less than half the previous level, close to pre-flight levels. Once the vitamin doses ceased, the uOC climbed back up again and remained high for the rest of the mission.

‘The fact that vitamin K restored normal levels of under-carboxylated osteocalcin proves that there is a lack of the vitamin in astronauts. We don’t know if there is a lack of vitamin K in the food, or if the metabolism of vitamin K is impaired,’ says Lafage-Proust. Their next step is to measure the effect of vitamin K metabolism on bone loss using microgravity simulations.

Benny Elmann-Larsen, a physiologist at the European Space Agency in Noordwijk, the Netherlands, thinks the research is very valuable. ‘If it can be demonstrated that vitamin K plays a role in the maintenance of bone mineral density, then it’s a very important finding,’ he says. Linda Shackelford, head of the Bone Lab at NASA’s Johnson Space Center in Houston, Texas, points out that bone loss in space is also related to the lack of mechanical loading on bones. ‘But it’s very important that we address all the possible mechanisms that contribute to bone loss,’ she says.

Author: Anil Ananthaswamy

Source: Clinical Chemistry (vol 46, p 1136)

New Scientist issue 9th September 2000

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