快猫短视频

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鈥攚hich is particularly abundant in broccoli鈥攎ay contribute
to bone loss in astronauts.

快猫短视频s have known that bone loss occurs in space, but the reasons have been unclear
(快猫短视频, 15 July, p 22). To try to understand the
mechanism, a team from the Jean Monnet University at Saint-脡tienne 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. 鈥淲e were very surprised. We thought the body
has some stocks of carboxylated osteocalcin. Apparently this is not the case,鈥�
says team member Marie-H茅l猫ne 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.

鈥淭he fact that vitamin K restored normal levels of under-carboxylated
osteocalcin proves that there is a lack of the vitamin in astronauts. We don鈥檛
know if there is a lack of vitamin K in the food, or if the metabolism of
vitamin K is impaired,鈥� 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. 鈥淚f it can be
demonstrated that vitamin K plays a role in the maintenance of bone mineral
density, then it鈥檚 a very important finding,鈥� he says. Linda Shackelford, head
of the Bone Lab at NASA鈥檚 Johnson Space Center in Houston, Texas, points out
that bone loss in space is also related to the lack of mechanical loading on
bones. 鈥淏ut it鈥檚 very important that we address all the possible mechanisms that
contribute to bone loss,鈥� she says.