The introduction of domesticated plants and animals into Britain during the Neolithic cultural period between 5,200 and 4,500 years ago is viewed either as a rapid event or as a gradual process that lasted for more than a millennium. Here we measure stable carbon isotopes present in bone to investigate the dietary habits of Britons over the Neolithic period and the preceding 3,800 years (the Mesolithic period). We find that there was a rapid and complete change from a marine- to a terrestrial-based diet among both coastal and inland dwellers at the onset of the Neolithic period, which coincided with the first appearance of domesticates. As well as arguing against a slow, gradual adoption of agriculture and animal husbandry by Mesolithic societies, our results indicate that the attraction of the new farming lifestyle must have been strong enough to persuade even coastal dwellers to abandon their successful fishing practices.
The change in subsistence at the Mesolithic/Neolithic transition in Denmark is often characterized as rapid, with a dramatic shift from a marine diet in the Mesolithic to a terrestrial-based diet in the Neolithic....
Marine diets are enriched in Vitamin D; some of the Pacific Northwest Indians consumed so much salmon that their children exhibited problems from excessive levels in their tissue! Though some meats, such as liver, as well as milk, also are non-trivial sources they are orders of magnitude less concentrated. There are debates about the usage of isotopes to extrapolate toward diets, but the tendency to rely upon marine sources seems rather common across Mesolithic Europe; with a relatively sharp shift toward domesticate animals and grains with the Neolithic revolution.
But here's something else I found, Cereal Grains: Humanity's Double-Edged Sword:
...In animal studies it has been long recognized that excessive consumption of cereal grains can induce vitamin D deficiencies in a wide variety of animals including primates. Epidemiological studies of populations consuming high levels of unleavened whole grain breads show vitamin D deficiency to be widespread. A study of radiolabelled 25-hydroxyvitamin D3 (25(OH)D3) in humans consuming 60 g of wheat bran daily for 30 days clearly demonstrated an enhanced elimination of 25(OH)D3 in the intestinal lume. The mechanism by which cereal grain consumption influences vitamin D is unclear. Some investigators have suggested that cereal grains may interfere with the enterohepatic circulation of vitamin D or its metabolites, whereas others have shown that calcium deficiency increases the rate of inactivation of vitamin D in the liver. This effect is mediated by 1,25-dihydroxyvitamin D (1,25(OH)2D) produced in response to
secondary hyperparathyroidism,which promotes hepatic conversion of vitamin D to polar inactivation products which are excreted in bile. Consequently, the low Ca/P ratio of cereal grains has the ability to elevate PTH which in turn stimulates increased production of 1,25(OH)2D which causes an accelerated loss of 25-hydroxyvitamin D.
So what you have here are two synergistic dynamics: the shift away from Vitamin D enriched foods combined with the reliance upon a staple which might actually reduce basal levels of this nutrient! OK, OK, I'm obsessed, right? To some extent yes, but, as with digestion of starch, I suspect a lot of recent human evolution is diet related. Because Vitamin D can be synthesized via exposure of skin to radiation the change in this nutrient might be particularly salient, but that does not mean that biochemical tweaks aren't just as important. In fact, it seems plausible that the variation in adaptations might show up in the range of disease susceptibilities we have as individuals and populations.
Some of the loci related to skin pigmentation show extremely powerful signatures of selection. This could be sexual selection. Or, it could be a byproduct of a nutritional deficiency as well as low sunlight levels. Ultimately, it doesn't matter that much. We do now though that we've probably gotten better at digesting starch and a substantial proportion of the world's population in western Eurasia can now digest lactose in adulthood because of a recent mutation. How many selective blasts can the genome take? I don't know, but I think we might have to forget about Haldane's Dilemma.
Related: Map of the spread of agriculture in Europe....