Putting vitamin D into the flour we buy could help stop tiredness, muscle aches and even heart failure, according to a study.
The UK weather means not all of us get enough of the "sunshine vitamin" between October and April.
Vitamin D's important for growing and strengthening our bones.
Researchers say adding it to wheat flour could stop 10 million deficiency cases in England and Wales over the next 90 years.
They say it could be done for 12p per person, per year.
One in five UK adults has a vitamin D deficiency, according to academics at the University of Birmingham.
Things like sun cream, air pollution and full-body clothing often stop people's skin from naturally making the vitamin in the sun.
The NHS says "everyone should consider" taking supplements during autumn and winter.
Not getting enough can cause tiredness, soft bones, bone pain, and muscle weakness - and in extreme cases, seizures or heart failure in babies and children.
The report says dark skin produces less vitamin D than white skin, but it's a common problem across the world - regardless of ethnicity.
It also says offering free supplements to "risk groups" like children, older people and black and ethnic minorities could stop more than three million further cases.
What else goes into our food?
The idea here's not new.
Iron's added to most kinds of flour in the UK - and has to be by law - to prevent conditions like anaemia, where someone doesn't produce enough red blood cells.
It's the same for calcium, which strengthens bones and helps our blood to clot when we get a cut.
Vegetarian and vegan soya products often have vitamin B added too - which breaks down food, gives us energy and keeps our eyes and skin healthy.
Lots of cereals already have vitamin D added, as does baby milk formula.
What else could be added to flour?
Vitamin D's not the only thing that's been suggested.
In June, the government said it was thinking about adding folic acid to flour - to help prevent birth defects.
That idea's aimed at stopping conditions like spina bifida - and the government is due to make a decision next year.
It's estimated it could stop around 200 cases a year.
Experts and government advisors say it's safe and will only bring benefits - lots of other countries have been doing it for years.
They say there's no evidence to back up concerns that high doses have caused symptoms like diarrhoea, sleep disorders and nausea.