54 | New Scientist | 26 September 2020Want to send us a question or answer?
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ANN^ &STEVE^ TOON/NATUREPL.COMSundown
How did people in the Arctic in the
distant past deal with no sun in
winter and weak sun the rest of the
year? Did food provide vitamin D?Roger Williams
Lucerne, Switzerland
According to the US National
Institutes of Health, 100 grams of
salmon or trout provides enough
daily vitamin D for adults of most
ages. This wouldn’t have been
hard for a hunter-gatherer to
find in Arctic Scandinavia, North
America or Russia.Guy Cox
School of medical sciences,
University of Sydney, Australia
The major dietary source of
vitamin D is oily fish, which was,
and is, a staple food in northern
latitudes (just try to separate a
Swede from pickled herrings).
So vitamin D deficiency wasn’t a
problem. In English slums, rickets
caused by vitamin D deficiency
was a major problem in the 19th
and early 20th century. Duringand after the second world war,
the UK government issued cod
liver oil to all children. Because of
this, rickets didn’t really exist at
the time. But the oil tasted awful.Mike Follows
Sutton Coldfield,
West Midlands, UK
Most people get the bulk of the
vitamin D they need from the
action of sunlight on their skin.
Ultraviolet light turns cholesterol
in the skin into vitamin D.
However, many indigenous
Arctic people have a dark
complexion that acts as a natural
sunscreen and makes getting
vitamin D this way more difficult.
While it is widely believed thatthey derive the vitamin D they
need from their diet, which
includes oily fish, the reality is
that their vitamin D levels are
lower than those of northern
Europeans, yet their skeletons
show no signs of rickets.
Vitamin D is biologically inert
and is converted into its active
form by a chemical reaction in the
liver and kidneys. Even though a
single exposure of UVB produces
less vitamin D in darker-skinned
people than in those with lighter
skin, it appears that the former
have adapted to be better at
converting vitamin D into its
active form. This may explain why
nearly half of African Americans
are classed as having a deficiency
in vitamin D, yet they show fewer
signs of the health impacts that
would usually result from this.David Muir
Edinburgh, UK
The traditional diet of Arctic
coastal indigenous people, like
the Inuit, is high in protein and fat
from marine mammals and fish.
Berries, roots and seaweed can
supply carbohydrate, but so does
fresh meat in the form of glycogen
when the meat is eaten raw.
Vital vitamins and minerals are
present in Inuit diets. More than
adequate amounts of vitamins A
and D are found in the livers
and oils of cold-water fish and
mammals, so the synthesis of
vitamin D in the skin through
exposure to the sun isn’t vital.
As the richest natural sources
of vitamin C are fruits and
vegetables, you would think that
getting enough of this might pose
a problem for Arctic indigenouscommunities. Once again, the
consumption of raw meat comes
to the rescue: vitamin C is present
in uncooked caribou liver, seal
brain and muktuk, a traditional
food of frozen whale skin and
blubber. If these were cooked, the
vitamin C would be destroyed.Cycle logic
A triplet bike is lighter and has less
resistance per person, so is more
efficient than a tandem, which is
more efficient than a regular bike.
Does this trend hold however long
the bike? (continued)Peter Mynors
London, UK
In 1962, I was one of five
undergraduates who cycled from
the UK to Greece – two of us on a
tandem and three on a triplet bike.
On level roads and moderate
uphill slopes, the triplet was
noticeably more efficient than the
tandem. On steeper hills, the main
influence on progress was how
soon one of the riders needed
to pause for breath and that
team had to stop.
Restarting either a tandem or
triplet on a steep uphill section
can be difficult, so we often
continued pushing that bike all
the way to the top. With a solo
bike, you can more easily remount
and ride on, which is one reason
why tandems are often regarded
as poor for climbing hills.
On the unsurfaced roads
through Yugoslavia, the longer
wheelbase of the triplet gave a
generally more comfortable ride,
at least for the middle rider.
With a well-matched team
of riders on the triplet, we found
it more efficient to have the
pedals displaced by 60 degrees
relative to the rider ahead, rather
than the usual arrangement
for tandems in which both
riders’ downstrokes occur
simultaneously, as the 60 degrees
setting provides constant power.This week’s new questions
Rainbow riot I have seen many double rainbows, but can you
get triple or quadruple ones? If so, where are the best places to
see them? What is the maximum number that could occur at
the same time? Carys Slack, Barry, South Glamorgan, UKShedding tears What is the biological advantage of crying
when emotional? Gary Greene, London, UKHow many rainbows
can you get all at the
same time?“ Raw meat comes to
the rescue: seal brain,
uncooked caribou
liver and muktuk,
made from whale
skin and blubber”